:root{--paper:#f6f6f6;--white:#ffffff;--ink:#353535;--muted:#848484;--line:#e6e6e6;--green:#505050;--dark:#343434;--lime:#e1e1e1;--light:#f1f1f1;--amber:#757575;--red:#696969;font-family:Inter,ui-sans-serif,-apple-system,BlinkMacSystemFont,"Segoe UI",sans-serif;color:var(--ink);font-synthesis:none}*{box-sizing:border-box}body{margin:0;background:var(--paper);font-size:14px}button,input,select{font:inherit}button,a,select{-webkit-tap-highlight-color:transparent}button{cursor:pointer}button:disabled{cursor:default;opacity:.42}button{transition:background .15s,transform .15s}button:focus-visible,a:focus-visible,select:focus-visible,input:focus-visible{outline:3px solid #9f9f9f;outline-offset:3px}button:hover:not(:disabled){filter:brightness(.96)}h1,h2,h3,h4,p{margin:0}button svg{flex-shrink:0}#app{display:flex;min-height:100vh}.sidebar{width:264px;background:var(--dark);color:#f3f3f3;padding:34px 18px 22px;display:flex;flex-direction:column;flex-shrink:0;position:fixed;inset:0 auto 0 0;overflow-y:auto}.brand{display:flex;align-items:center;gap:13px;padding:0 13px;text-decoration:none;color:inherit;font-size:26px;font-weight:600;letter-spacing:-1px}.brand-light{color:#e1e1e1;font-weight:400}.brand-mark{color:var(--lime);font-family:Georgia,serif;font-size:30px;letter-spacing:-3px;border:1px solid #ffffff27;border-radius:11px;width:43px;height:43px;display:grid;place-items:center}.brand small{display:block;font-size:7px;font-weight:500;letter-spacing:1.25px;color:#bebebe;margin-top:5px}.course-label{background:#ffffff08;border:1px solid #ffffff13;border-radius:8px;padding:12px 15px;margin:31px 10px 34px;font-size:11px;color:#dadada;display:flex;align-items:center;gap:9px}.course-label span:not(.course-dot){opacity:.4}.course-dot,.tiny-dot{width:6px;height:6px;display:inline-block;background:#cccccc;border-radius:50%}.nav-label{font-size:9px;letter-spacing:1.4px;color:#aaaaaa;margin:0 14px 14px}.topic{border:0;background:none;color:#cbcbcb;width:100%;padding:13px 11px;margin-bottom:6px;display:flex;gap:12px;align-items:center;text-align:left;border-radius:8px;position:relative}.topic strong{font-size:12px;font-weight:500;display:block;line-height:1.4}.topic small{display:block;font-size:9px;color:#a6a6a6;margin-top:4px}.topic-symbol{font-family:Georgia,serif;font-size:20px;width:25px;flex-shrink:0;text-align:center;line-height:1}.topic.active{background:#e9e9e9;color:#3e3e3e}.topic.active small{color:#7a7a7a}.active-dot{background:var(--green);width:5px;height:5px;border-radius:50%;position:absolute;right:12px;top:17px}.sidebar-note{border-top:1px solid #ffffff15;margin:42px 14px 25px;padding-top:23px}.note-icon{color:#d7d7d7;margin-bottom:13px}.sidebar-note h3{font-family:Georgia,serif;font-weight:400;font-size:20px}.sidebar-note p{font-size:11px;line-height:1.8;color:#bbbbbb;margin-top:10px}.sidebar-bottom{display:flex;align-items:center;gap:8px;margin:auto 14px 0;padding-top:20px;color:#bfbfbf;font-size:10px}.sidebar-bottom .tiny-dot{margin-left:auto;background:#b2b2b2;width:5px;height:5px}.main{margin-left:264px;width:calc(100% - 264px)}.topbar{height:79px;border-bottom:1px solid var(--line);display:flex;justify-content:space-between;align-items:center;padding:0 45px;font-size:11px;color:#919191;background:#fafafa}.topbar>div>span{margin:0 13px;color:#c5c5c5}.topbar strong{font-weight:500;color:#636363}.topbar-right{display:flex;align-items:center;gap:17px}.topbar-right .private-badge{display:flex;align-items:center;gap:5px;font-size:10px;color:#8a8a8a;margin:0}.language{display:flex;border:1px solid #e0e0e0;border-radius:7px;padding:3px;gap:2px}.language button{font-size:10px;background:transparent;color:#858585;border:0;border-radius:4px;padding:5px 8px;font-weight:500}.language .selected{background:#e8e8e8;color:#464646}.topbar-right .avatar{width:30px;height:30px;margin:0;color:#6a6a6a;background:#eaeaea;display:grid;place-items:center;border-radius:50%;font-family:Georgia,serif;font-size:15px}main{padding:41px 45px 0;max-width:1480px;margin:auto}.intro{display:flex;justify-content:space-between;gap:20px;align-items:center;margin-bottom:30px}.eyebrow{font-size:8px;font-weight:600;letter-spacing:1.6px;color:#828282;display:flex;align-items:center;gap:7px}.eyebrow>span{width:5px;height:5px;border-radius:50%;background:#828282}h1{font-family:Georgia,"Times New Roman",serif;font-size:37px;font-weight:400;letter-spacing:-1.2px;line-height:1.2;margin-top:13px}.intro p{color:#919191;font-size:12px;margin-top:11px}.practice-stat{display:flex;align-items:center;gap:12px;margin-left:10px;padding-top:20px}.practice-stat>span:first-child{font-size:36px;font-weight:300;color:#4d4d4d;letter-spacing:-2px}.practice-stat>div{font-size:9px;line-height:1.6;color:#8e8e8e;white-space:nowrap}.stat-star{font-size:34px;color:#c7c7c7;margin-left:5px}.workspace{display:grid;grid-template-columns:minmax(0,1fr) 273px;gap:25px;align-items:start}.practice-column{min-width:0}.controls{display:flex;gap:18px;align-items:end;background:#f0f0f0;border:1px solid #e4e4e4;border-radius:10px;padding:17px 20px;margin-bottom:18px}.controls label{font-size:8px;letter-spacing:1.1px;font-weight:600;color:#858585;display:flex;flex-direction:column;gap:7px}.controls select{border:0;background:transparent;color:#4a4a4a;font-size:11px;min-width:124px;padding:0 22px 0 0;cursor:pointer}.controls label:nth-child(2) select{min-width:75px}.quiet{background:transparent;border:1px solid #dcdcdc;border-radius:6px;padding:9px 12px;color:#5f5f5f;font-size:10px;display:flex;gap:7px;align-items:center}.new-set{margin-left:auto;border:0;padding:2px 0 2px 8px;white-space:nowrap;font-size:10px}.exercise-card{background:var(--white);border:1px solid #e3e3e3;border-radius:12px;box-shadow:0 3px 5px #34343403;overflow:hidden;padding:26px 30px 0}.exercise-heading{display:flex;justify-content:space-between;align-items:center;gap:10px}.pill{font-size:8px;letter-spacing:1.05px;color:#6f6f6f;background:#f0f0f0;padding:6px 9px;border-radius:4px;font-weight:600}.exercise-meta{font-size:9px;color:#9d9d9d;display:flex;gap:8px}h2{font-size:21px;font-weight:500;letter-spacing:-.5px}.exercise-card>h2{margin-top:18px}.goal{font-size:11px;line-height:1.7;color:#919191;margin-top:7px}.problem-display{display:flex;align-items:center;justify-content:center;gap:20px;padding:23px 10px 26px;min-height:154px;overflow-x:auto}.matrix-name{font-family:Georgia,serif;font-style:italic;font-size:21px;white-space:nowrap}.matrix-wrap{display:inline-block;position:relative;padding:5px 11px;margin:4px 1px;flex-shrink:0}.matrix-wrap:before,.matrix-wrap:after{content:"";position:absolute;top:0;bottom:0;width:7px;border-top:1.5px solid #7b7b7b;border-bottom:1.5px solid #7b7b7b}.matrix-wrap:before{left:0;border-left:1.5px solid #7b7b7b}.matrix-wrap:after{right:0;border-right:1.5px solid #7b7b7b}.matrix-grid{display:grid;grid-template-columns:repeat(var(--cols),minmax(27px,auto));row-gap:5px;column-gap:5px}.matrix-cell{font-family:"Cambria Math",Georgia,serif;font-size:20px;min-width:29px;padding:3px 5px;text-align:center;line-height:1.25;white-space:nowrap;font-variant-numeric:tabular-nums}.matrix-cell.split{border-left:1px solid #9b9b9b;margin-left:5px;padding-left:10px}.matrix-caption{border-left:1px solid #e5e5e5;padding-left:20px;color:#a6a6a6;font-size:9px;line-height:1.9;max-width:175px}.sign-inline{display:block;font-size:17px;font-weight:400;color:#8b8b8b;margin-top:4px}#step-area{border-top:1px solid var(--line);margin:0 -30px;padding:22px 30px 0}.step-head{display:flex;justify-content:space-between;align-items:center;gap:15px;font-size:8px;letter-spacing:1px;color:#7b7b7b;font-weight:600;margin-bottom:13px}.of{color:#ababab;margin-left:2px}.step-dots{display:flex;gap:4px;max-width:65%;flex-wrap:wrap;justify-content:end}.step-dots i{width:13px;height:3px;border-radius:3px;background:#ebebeb}.step-dots .here{background:#878787}.step-dots .complete{background:#c9c9c9}.step-head+h3{font-size:15px;letter-spacing:-.2px;font-weight:500}.step-instruction{font-size:11px;line-height:1.75;color:#848484;margin-top:8px;max-width:600px}.step-matrix{display:flex;align-items:center;gap:16px;margin-top:16px;overflow-x:auto;padding:2px 0 5px}.step-matrix>span{font-size:9px;color:#8c8c8c;max-width:180px;line-height:1.8}.small .matrix-cell{font-size:15px;min-width:24px;padding:3px 5px}.small .matrix-grid{column-gap:3px;row-gap:2px}.matrix-cell.diagonal{background:#e8e8e8;color:#4c4c4c;border-radius:3px}.matrix-cell.repeated{color:#a9a9a9}.matrix-cell.repeated.diagonal{color:#626262;background:#f0f0f0}.matrix-cell.target{background:#f0f0f0}.matrix-cell.source{background:#efefef;color:#6d6d6d}.matrix-cell.pivot{outline:1px solid #c0c0c0;outline-offset:-1px}.matrix-cell.deleted{color:#b8b8b8;background:#f1f1f1;text-decoration:line-through;text-decoration-color:#9a9a9a}.minor-preview{display:flex;align-items:center;gap:25px;margin-top:18px;overflow-x:auto}.minor-preview>span{color:#b6b6b6}.legend-target,.legend-source{display:inline-block;width:6px;height:6px;border-radius:2px;background:#dadada;margin:0 4px 0 7px}.legend-source{background:#c8c8c8}.answer-label{font-size:8px;letter-spacing:1px;color:#9a9a9a;margin-top:20px;margin-bottom:9px;font-weight:600}.answer-grid{display:grid;grid-template-columns:repeat(var(--answer-cols),minmax(0,1fr));gap:10px;max-width:500px}.answer-cell{display:flex;flex-direction:column;gap:5px;position:relative}.answer-cell>span:first-child{font-size:9px;color:#868686}.answer-cell input{border:1px solid #dfdfdf;background:#fcfcfc;padding:10px 11px;width:100%;border-radius:6px;color:#494949;font-family:Georgia,serif;font-size:18px;height:43px;transition:border-color .1s}.answer-cell input::placeholder{color:#bdbdbd}.answer-cell input.correct{border-color:#ababab;background:#f6f6f6}.answer-cell input.incorrect{border-color:#a5a5a5;background:#fbfbfb}.answer-grid.single{max-width:220px}.single .answer-cell{display:grid;grid-template-columns:auto 1fr;align-items:center;gap:12px}.single .answer-cell>span:first-child{font-family:Georgia,serif;font-size:18px;font-style:italic;color:#696969}.cell-result{font-size:8px;min-height:10px}.single .cell-result{position:absolute;top:15px;right:8px;min-height:0}.cell-result.ok{color:#727272}.cell-result.bad{color:#717171}.single .cell-result.bad{font-size:7px;background:#fbfbfb}.format-note{font-size:9px;color:#a8a8a8;margin-top:10px;line-height:1.6}.feedback{min-height:25px;font-size:10px;line-height:1.6;margin-top:10px;padding:3px 0}.feedback.success{color:#757575}.feedback.error{color:#6d6d6d}.step-actions{display:flex;align-items:center;gap:20px;margin-top:4px;margin-bottom:24px}.primary{border:0;background:var(--green);color:#fbfbfb;border-radius:6px;font-size:11px;padding:12px 16px;display:inline-flex;align-items:center;gap:20px;justify-content:space-between;min-height:41px}.hint-button{background:none;border:0;color:#8d8d8d;font-size:10px;display:flex;align-items:center;gap:6px;padding:8px 0}.step-bottom{margin:0 -30px;border-top:1px solid #efefef;padding:15px 30px;display:flex;justify-content:space-between;gap:10px;background:#fefefe}.text-button{border:0;background:none;color:#9b9b9b;padding:0;font-size:9px;display:flex;align-items:center;gap:6px}.hint-box{background:#f6f6f6;border:1px solid #e5e5e5;color:#808080;border-radius:7px;font-size:11px;line-height:1.7;padding:12px 14px;margin-bottom:20px}.hint-box p{display:flex;gap:8px;margin:4px 0}.hint-box svg{flex-shrink:0;margin-top:3px}.problem-strip{display:flex;align-items:center;justify-content:space-between;gap:15px;margin-top:19px}.problem-strip>span{font-size:8px;letter-spacing:1px;color:#9c9c9c;font-weight:500}.problem-strip>div{display:flex;gap:6px}.problem-number{width:28px;height:28px;border:1px solid #e4e4e4;border-radius:5px;background:transparent;color:#9b9b9b;font-size:10px}.problem-number.current{background:#ececec;border-color:#c5c5c5;color:#6c6c6c}.problem-number.finished{background:#595959;color:white}.save-note{margin-top:20px;color:#a9a9a9;font-size:9px;display:flex;align-items:center;gap:6px}.reference{background:#f1f1f1;border:1px solid #e4e4e4;border-radius:10px;padding:22px 20px}.reference-title{display:flex;align-items:center;gap:8px;color:#6c6c6c}.reference-title h2{font-size:14px;letter-spacing:-.2px;font-weight:500}.reference-tabs{display:flex;border-bottom:1px solid #e0e0e0;margin-top:18px;margin-bottom:22px}.reference-tabs button{flex:1;font-size:9px;color:#989898;background:none;border:0;padding:0 0 11px;position:relative;white-space:nowrap}.reference-tabs button.selected{color:#5f5f5f}.reference-tabs button.selected:after{content:'';height:2px;background:#8c8c8c;position:absolute;bottom:-1px;left:0;right:0}#reference-content h3{font-size:13px;font-weight:500;letter-spacing:-.3px;line-height:1.5}#reference-content p{font-size:10px;color:#949494;line-height:1.8;margin-top:8px}.checkerboard{display:grid;grid-template-columns:repeat(4,1fr);gap:4px;margin:19px auto 13px;max-width:180px}.checkerboard span{display:grid;place-items:center;height:34px;border-radius:4px;font-family:Georgia,serif;font-size:21px;font-weight:400}.checkerboard .positive{background:#e5e5e5;color:#868686}.checkerboard .negative{background:#eaeaea;color:#9f9f9f}.formula{text-align:center;font-family:Georgia,serif;font-size:15px;color:#8e8e8e;margin:15px 0}.formula sup{font-size:9px}.reference-divider{height:1px;background:#e2e2e2;margin:21px 0}#reference-content h4{font-size:11px;font-weight:500}.example-math{background:#eaeaea;border-radius:5px;padding:11px;text-align:center;font-family:Georgia,serif;font-size:18px;color:#878787;margin-top:13px}.reference-foot{text-align:center;font-size:9px!important}.tip-card{margin-top:24px;background:#eaeaea;border:1px solid #e1e1e1;border-radius:7px;padding:14px}.tip-label{font-size:7px;letter-spacing:.9px;color:#979797;display:flex;gap:6px;align-items:center;font-weight:600}.tip-card p{font-size:9px;color:#979797;line-height:1.8;margin-top:9px}.row-rule{display:flex;gap:12px;margin-top:19px}.row-rule>b{font-size:10px;color:#a5a5a5;background:#e6e6e6;border-radius:4px;height:25px;width:25px;display:grid;place-items:center;flex-shrink:0}.row-rule strong{font-weight:500;font-size:10px;line-height:1.6}.row-rule p{font-size:9px!important;margin-top:3px!important}.completion{padding:5px 0 35px;text-align:center}.completion-check{display:inline-flex;background:#efefef;padding:12px;border-radius:50%;color:#7d7d7d}.completion h3{font-family:Georgia,serif;font-size:25px;font-weight:400;margin-top:15px}.completion p{font-size:12px;line-height:1.8;color:#929292;margin-top:10px}.completion .primary{margin:20px auto 16px}.completion .text-button{margin:auto}.solution-card{background:#ffffff;border:1px solid var(--line);border-radius:12px;padding:28px 30px;margin-top:30px}.solution-heading h2{font-family:Georgia,serif;font-size:29px;font-weight:400;margin-top:10px}.solution-heading p{font-size:11px;color:#9e9e9e;margin-top:9px}.solution-list{list-style:none;padding:0;margin:25px 0}.solution-list>li{display:flex;gap:20px;padding:21px 0;border-top:1px solid #eeeeee}.solution-list>li>div{min-width:0;overflow-x:auto;flex:1}.solution-number{background:#f1f1f1;color:#909090;border-radius:50%;width:25px;height:25px;display:grid;place-items:center;font-size:11px;flex-shrink:0}.solution-list h3{font-size:14px;font-weight:500;margin-top:2px}.solution-list p{font-size:11px;line-height:1.8;color:#949494;margin-top:8px}.worked-math{font-family:Georgia,serif;font-size:16px;color:#727272;line-height:1.7;margin:12px 0;overflow-wrap:anywhere}.calculations{display:flex;gap:10px;flex-wrap:wrap;margin:12px 0}.calculations code{font-family:Georgia,serif;font-size:13px;padding:7px 10px;background:#f5f5f5;color:#868686;border-radius:4px}.solution-answer{font-family:Georgia,serif;color:#959595;font-size:14px;line-height:1.8}footer{display:flex;justify-content:space-between;gap:20px;border-top:1px solid var(--line);padding:22px 0 24px;margin-top:33px;font-size:8px;color:#afafaf}footer span span{margin:0 6px;color:#c3c3c3}
@media(min-width:1500px){main{padding:48px 60px 0}.workspace{grid-template-columns:minmax(0,1fr) 300px;gap:30px}.reference{padding:25px}.exercise-card{padding:29px 36px 0}#step-area{margin:0 -36px;padding:25px 36px 0}.step-bottom{margin:0 -36px;padding:16px 36px}h1{font-size:42px}.goal,.step-instruction{font-size:12px}.topic strong{font-size:13px}.reference-tabs button{font-size:10px}.matrix-cell{font-size:23px;min-width:35px}.problem-display{padding:26px 10px 30px}}
@media(max-width:1200px){.sidebar{width:230px;padding-left:12px;padding-right:12px}.main{margin-left:230px;width:calc(100% - 230px)}.brand{font-size:24px}.topbar{padding:0 28px}main{padding:32px 28px 0}.workspace{gap:18px;grid-template-columns:minmax(0,1fr) 235px}.reference{padding:20px 16px}.controls{padding:15px;gap:10px}.new-set{font-size:9px}.exercise-card{padding:23px 23px 0}#step-area{margin:0 -23px;padding:22px 23px 0}.step-bottom{margin:0 -23px;padding:15px 23px}.matrix-caption{display:none}h1{font-size:31px}.practice-stat{gap:8px}.practice-stat .stat-star{display:none}.problem-strip{align-items:start;flex-direction:column;gap:10px}.topic strong{font-size:11px}}
@media(max-width:1000px){.workspace{grid-template-columns:minmax(0,1fr)}.reference{display:block}.controls select{min-width:125px}h1{font-size:34px}.practice-stat{display:none}.matrix-caption{display:block}.problem-strip{flex-direction:row;align-items:center}}
@media(max-width:700px){#app{display:block}.sidebar{position:static;width:100%;padding:20px 20px 0;overflow:visible}.brand{font-size:23px;padding:0}.brand small{font-size:6px}.brand-mark{height:37px;width:37px;font-size:27px}.course-label,.nav-label,.sidebar-note,.sidebar-bottom{display:none}.sidebar nav{display:flex;overflow-x:auto;gap:7px;margin:19px -20px 0;padding:0 20px 14px;scrollbar-width:thin}.topic{width:auto;flex-shrink:0;gap:7px;padding:9px 11px;margin:0;background:#ffffff0b;white-space:nowrap}.topic-symbol{width:18px;font-size:17px}.topic strong{font-size:10px}.topic small{display:none}.active-dot{display:none}.main{width:100%;margin:0}.topbar{height:56px;padding:0 20px}.topbar>div:first-child{font-size:9px}.topbar>div:first-child>span{margin:0 8px}.topbar>div:first-child strong{display:none}.topbar-right{gap:12px}.topbar-right .avatar{display:none}.topbar-right .private-badge{font-size:9px}.language button{font-size:9px;padding:4px 7px}main{padding:27px 20px 0}.intro{margin-bottom:24px}.eyebrow{font-size:7px;letter-spacing:1.2px}h1{font-size:32px;max-width:350px;line-height:1.17;margin-top:12px}.intro p{font-size:11px;line-height:1.8;max-width:280px;margin-top:12px}.controls{gap:14px;padding:14px;border-radius:8px;align-items:center}.controls label{font-size:7px;letter-spacing:.6px;gap:7px}.controls select{font-size:10px;min-width:99px}.controls label:nth-child(2) select{min-width:55px}.new-set{font-size:0;padding:6px;margin-left:auto}.new-set svg{width:17px;height:17px}.exercise-card{padding:22px 19px 0;border-radius:10px}.exercise-meta{font-size:8px}.exercise-card>h2{font-size:20px}.goal{font-size:10px}.problem-display{gap:13px;padding:23px 0;justify-content:center}.matrix-caption{display:none}.matrix-name{font-size:18px}.matrix-cell{font-size:18px;min-width:24px;padding:2px 3px}.matrix-grid{column-gap:2px;row-gap:3px}#step-area{margin:0 -19px;padding:20px 19px 0}.step-bottom{margin:0 -19px;padding:15px 19px}.step-head+h3{font-size:14px}.step-instruction{font-size:11px}.step-matrix{gap:10px;flex-wrap:wrap}.step-matrix>span{max-width:100%;font-size:8px}.small .matrix-cell{font-size:13px;min-width:21px;padding:3px}.small .matrix-grid{gap:2px}.matrix-cell.split{padding-left:7px;margin-left:3px}.step-actions{gap:14px}.primary{font-size:10px;padding:12px 13px;gap:14px}.hint-button{font-size:9px;gap:4px}.format-note{font-size:8px}.text-button{font-size:8px}.answer-grid{gap:8px}.answer-cell>span:first-child{font-size:8px}.answer-cell input{padding:10px 8px;font-size:15px}.answer-label{font-size:7px}.feedback{font-size:9px}.step-dots i{width:10px}.problem-strip{flex-direction:column;align-items:start;gap:10px}.problem-number{width:30px;height:30px}.save-note{font-size:8px;line-height:1.7}.reference{display:block;margin-top:6px;padding:20px}.reference-title h2{font-size:15px}.reference-tabs button{font-size:11px}#reference-content h3{font-size:14px}#reference-content p{font-size:11px}.checkerboard{max-width:195px}.reference{max-width:none}.reference-foot{font-size:10px!important}.tip-card p{font-size:10px}.workspace{gap:20px}.solution-card{padding:24px 18px}.solution-list>li{gap:12px}.worked-math{font-size:14px}.solution-list h3{font-size:13px}.solution-heading h2{font-size:26px}.solution-heading p{line-height:1.8}footer{flex-direction:column;gap:8px;padding:20px 0;margin-top:26px;font-size:8px}}
@media(prefers-reduced-motion:reduce){*{scroll-behavior:auto!important;transition:none!important}}
.problem-display{justify-content:safe center}.matrix-name{flex-shrink:0}
.goal,.step-instruction{font-size:13px;color:#777777}.intro p{color:#7c7c7c}
#reference-content p{font-size:11px;color:#797979}.reference-foot{color:#797979}
.tip-card p{font-size:10px;color:#797979}.format-note{font-size:10px;color:#828282}
.matrix-caption,.step-matrix>span{color:#818181}.text-button{color:#7c7c7c}
.save-note{color:#818181}.reference-tabs button{color:#7b7b7b}.reference-tabs button.selected{color:#515151}
@media(max-width:700px){.goal,.step-instruction{font-size:12px}.format-note{font-size:9px}.problem-display{justify-content:safe center}}
@media(max-width:700px){.problem-display:has(.split){flex-direction:column;gap:8px}}
[hidden]{display:none!important}.sr-only{position:absolute;width:1px;height:1px;padding:0;margin:-1px;overflow:hidden;clip:rect(0,0,0,0);white-space:nowrap;border:0}.worked-math{white-space:pre-line}
.topic>span:nth-child(2){min-width:0;flex:1;padding-right:5px}.topic strong{overflow-wrap:break-word}.solution-summary{margin-top:24px;background:#f3f3f3;border:1px solid #e3e3e3;border-radius:8px;padding:18px 20px;overflow:hidden}.summary-label{font-size:8px;font-weight:600;letter-spacing:1px;color:#8a8a8a}.solution-summary>div{display:flex;align-items:center;gap:15px;overflow-x:auto;margin-top:8px}.solution-summary .worked-math{margin:0;font-size:18px}.solution-summary .matrix-name{font-size:18px}
.progress-open{border:0;background:none;color:#797979;font-size:10px;padding:7px 3px}.exam-toggle{border:1px solid #dbdbdb;background:#f9f9f9;color:#717171;border-radius:6px;padding:8px 11px;font-size:9px;display:flex;align-items:center;gap:7px;white-space:nowrap}.exam-toggle.on{background:#ececec;border-color:#c4c4c4;color:#515151}.exam-dot{width:6px;height:6px;border-radius:50%;background:#a7a7a7;display:inline-block}.exam-toggle.on .exam-dot{background:#8b8b8b;box-shadow:0 0 0 3px #dfdfdf}.exam-timer{font-family:ui-monospace,monospace;font-size:10px;color:#7d7d7d;white-space:nowrap}.sandbox-panel{margin-top:22px;padding-top:18px;border-top:1px solid #e3e3e3}.sandbox-panel summary{list-style:none;cursor:pointer;display:flex;align-items:center;gap:7px;color:#747474;font-size:11px;font-weight:500}.sandbox-panel summary::-webkit-details-marker{display:none}.sandbox-panel>p{font-size:10px;line-height:1.7;color:#8c8c8c;margin-top:10px}.sandbox-controls{display:flex;align-items:center;gap:8px;flex-wrap:wrap;margin-top:13px}.sandbox-controls label{display:flex;align-items:center;gap:5px;color:#727272;font-family:Georgia,serif;font-size:13px}.sandbox-controls select,.sandbox-controls input{border:1px solid #dadada;background:#ffffff;border-radius:4px;color:#5f5f5f;padding:5px 6px;font-family:Georgia,serif;font-size:13px;min-width:39px}.sandbox-controls input{width:59px}.sandbox-controls button{font-size:9px;padding:8px 10px}.sandbox-status{min-height:17px;margin-top:10px;font-size:9px;color:#828282;line-height:1.6}.sandbox-status.error{color:#6e6e6e}.sandbox-status.success{color:#6f6f6f}.sandbox-result{overflow-x:auto;margin-top:4px}.progress-modal{position:fixed;z-index:20;inset:0;display:grid;place-items:center}.progress-backdrop{position:absolute;inset:0;background:#34343466;backdrop-filter:blur(3px)}.progress-dialog{position:relative;z-index:1;width:min(430px,calc(100% - 34px));background:#ffffff;border:1px solid #e2e2e2;border-radius:12px;padding:28px;box-shadow:0 14px 60px #34343440}.progress-close{position:absolute;right:16px;top:12px;background:none;border:0;color:#909090;font-size:22px}.progress-dialog h2{font-family:Georgia,serif;font-size:28px;font-weight:400;margin-top:10px}.progress-lead{font-size:11px;color:#909090;line-height:1.7;margin-top:8px}.progress-total{display:flex;align-items:baseline;gap:10px;margin:22px 0 17px;padding:15px;background:#f1f1f1;border-radius:7px}.progress-total strong{font-family:Georgia,serif;font-size:33px;font-weight:400;color:#666666}.progress-total span{font-size:10px;color:#808080}.progress-list{border-top:1px solid #eaeaea}.progress-row{display:flex;justify-content:space-between;align-items:center;padding:11px 3px;border-bottom:1px solid #f0f0f0;font-size:10px;color:#7c7c7c}.progress-row strong{font-family:Georgia,serif;font-size:16px;color:#7a7a7a}.progress-note{font-size:9px;line-height:1.7;color:#a1a1a1;margin:17px 0}.progress-dialog>.quiet{font-size:10px}
.mode-switch{display:flex;gap:4px;padding:4px;border:1px solid #e1e1e1;background:#f0f0f0;border-radius:9px;margin-bottom:18px}.mode-switch button{flex:1;display:flex;align-items:center;justify-content:center;gap:10px;border:0;border-radius:6px;background:none;color:#7e7e7e;padding:12px;font-size:11px}.mode-switch button.selected{background:#ffffff;color:#525252;box-shadow:0 2px 5px #34343408}.mode-switch button span{font-size:7px;letter-spacing:1px;background:#e6e6e6;color:#7c7c7c;border-radius:3px;padding:3px 4px}
.custom-editor{background:#ffffff;border:1px solid #dedede;border-top:3px solid #b1b1b1;border-radius:10px;padding:26px;margin-bottom:20px}.custom-heading{display:flex;align-items:center;justify-content:space-between;gap:16px}.custom-heading h2{font-family:Georgia,serif;font-weight:400;font-size:25px;margin-top:9px}.custom-chip{font-family:Georgia,serif;font-size:18px;font-style:italic;background:#f2f2f2;color:#808080;border:1px solid #e5e5e5;border-radius:6px;white-space:nowrap;padding:8px 12px}.custom-intro{font-size:12px;color:#838383;line-height:1.8;margin-top:10px}.custom-controls{display:flex;gap:16px;flex-wrap:wrap;margin-top:23px;padding-bottom:20px;border-bottom:1px solid #ececec}.custom-controls label{display:flex;flex-direction:column;gap:7px;font-size:8px;letter-spacing:.8px;color:#909090}.custom-controls select{color:#5a5a5a;background:#f6f6f6;border:1px solid #e5e5e5;border-radius:5px;padding:7px 23px 7px 8px;font-size:11px;max-width:240px}.custom-controls label:nth-child(2){flex:1}.custom-controls label:nth-child(2) select{width:100%}.custom-grid-scroll{overflow-x:auto;padding:21px 0 5px}.custom-grid{display:grid;grid-template-columns:repeat(var(--n),minmax(45px,1fr)) minmax(55px,1fr);gap:9px;max-width:580px;margin:auto}.custom-col-label{font-family:Georgia,serif;font-style:italic;text-align:center;font-size:15px;color:#8b8b8b}.custom-grid .rhs{padding-left:12px;border-left:1px solid #cecece}.custom-grid label{min-width:0}.custom-grid input{width:100%;min-width:0;text-align:center;padding:10px 3px;border:1px solid #dfdfdf;border-radius:5px;font-family:Georgia,serif;color:#535353;font-size:17px;background:#fbfbfb;height:41px}.custom-grid .rhs input{background:#f2f2f2}.custom-grid input[aria-invalid=true]{border-color:#737373;background:#f4f4f4}.custom-format{font-size:10px;color:#888888;line-height:1.8;margin:10px 0 18px}.paste-panel{border:1px solid #e7e7e7;background:#fbfbfb;border-radius:6px;padding:12px 14px}.paste-panel summary{cursor:pointer;color:#787878;font-size:11px}.paste-panel p{font-size:11px;line-height:1.8;color:#8f8f8f;margin-top:12px}.paste-panel textarea{width:100%;resize:vertical;margin:10px 0;border:1px solid #dcdcdc;padding:12px;border-radius:5px;font-family:monospace;font-size:13px;line-height:1.6;color:#595959;background:#ffffff}.paste-panel textarea::placeholder{color:#b6b6b6}.custom-status{font-size:10px;color:#888888;line-height:1.8;min-height:36px;margin:15px 0 10px}.custom-status.error{color:#676767}.custom-actions{display:flex;align-items:center;gap:12px;flex-wrap:wrap}.custom-actions .quiet{padding:12px;font-size:11px}
@media(max-width:1200px){.custom-controls label:nth-child(3){width:100%}.custom-controls label:nth-child(3) select{max-width:none}.custom-controls{gap:12px}.custom-grid{gap:6px}}
@media(max-width:700px){.mode-switch button{font-size:10px;padding:10px 4px;gap:5px}.mode-switch button span{font-size:6px}.custom-editor{padding:19px 16px}.custom-heading h2{font-size:23px}.custom-chip{display:none}.custom-intro{font-size:11px}.custom-controls select{font-size:10px;max-width:205px}.custom-grid{grid-template-columns:repeat(var(--n),minmax(35px,1fr)) minmax(43px,1fr);gap:6px}.custom-grid input{font-size:15px}.custom-grid .rhs{padding-left:6px}.custom-actions{gap:10px}.custom-actions .quiet{font-size:10px}.custom-format{font-size:9px}}
html,body{overflow-x:hidden}
.sound-control{display:flex;align-items:center;gap:4px}.sound-toggle{border:0;background:none;color:#7c7c7c;font-size:14px;padding:5px 3px;line-height:1;cursor:pointer}.sound-toggle[aria-pressed="false"]{opacity:.55}.sound-control input[type="range"]{accent-color:#8c8c8c;width:55px;height:15px;cursor:pointer}
@media(max-width:700px){.sound-control input[type="range"]{width:42px}.sound-toggle{font-size:13px}}
.progress-row span{display:flex;flex-direction:column;gap:3px}.progress-row small{font-size:8px;color:#a2a2a2;font-weight:400}.focus-card{margin-top:18px;padding:15px;background:#f4f4f4;border:1px solid #e4e4e4;border-radius:8px}.focus-label{display:block;font-size:7px;letter-spacing:1px;color:#909090;font-weight:600}.focus-card strong{display:block;font-family:Georgia,serif;font-size:16px;font-weight:400;color:#666666;margin-top:7px}.focus-card p{font-size:10px;line-height:1.7;color:#8e8e8e;margin-top:6px}.focus-card .primary{font-size:10px;padding:9px 12px;min-height:35px;margin-top:12px;gap:12px}.solution-actions{display:flex;align-items:center;justify-content:space-between;gap:15px;flex-wrap:wrap;border-top:1px solid #eeeeee;padding-top:15px}.solution-actions .quiet{font-size:10px}
@media print{body{background:#ffffff}.sidebar,.topbar,.intro,.controls,.mode-switch,.problem-strip,.save-note,.reference,footer,#step-area,.exercise-heading,.goal,.problem-display,.solution-actions button#close-solution{display:none!important}.main{margin:0;width:100%}main{padding:0;max-width:none}.workspace{display:block}.practice-column{display:none}#solution-area{display:block}.solution-card{border:0;margin:0;padding:0;box-shadow:none}.solution-heading h2{font-size:26px}.solution-heading p{color:#555555}.solution-list>li{break-inside:avoid}.worked-math,.solution-answer{color:#222222}.calculations code{background:#f3f3f3;color:#222222}}
.tools-open{border:1px solid #dfdfdf;background:#f9f9f9;color:#686868;border-radius:6px;font-size:10px;padding:7px 10px;white-space:nowrap}.tools-modal{position:fixed;z-index:30;inset:0;display:grid;place-items:center}.tools-backdrop{position:absolute;inset:0;background:#34343466;backdrop-filter:blur(3px)}.tools-dialog{position:relative;z-index:1;width:min(720px,calc(100% - 30px));max-height:min(760px,calc(100% - 30px));overflow:auto;background:#ffffff;border:1px solid #e2e2e2;border-radius:13px;padding:28px;box-shadow:0 14px 60px #34343440}.tools-close{position:absolute;right:16px;top:12px;background:none;border:0;color:#909090;font-size:22px}.tools-dialog h2{font-family:Georgia,serif;font-size:28px;font-weight:400;margin-top:10px}.tools-lead{font-size:11px;line-height:1.7;color:#909090;margin-top:8px}.tools-tabs{display:flex;gap:4px;border-bottom:1px solid #e7e7e7;margin-top:20px}.tools-tabs button{border:0;background:none;color:#919191;font-size:10px;padding:10px 13px;position:relative}.tools-tabs button.selected{color:#5c5c5c}.tools-tabs button.selected:after{content:'';height:2px;background:#8c8c8c;position:absolute;left:0;right:0;bottom:-1px}.tool-pane{padding-top:19px}.tool-grid{display:grid;grid-template-columns:1fr 1fr;gap:12px}.tool-grid label,.tool-pane>label{display:flex;flex-direction:column;gap:7px;font-size:9px;letter-spacing:.8px;color:#7d7d7d;font-weight:600}.tool-grid textarea,.tool-pane>label textarea{resize:vertical;border:1px solid #dddddd;background:#fcfcfc;border-radius:6px;padding:10px;font:14px/1.6 ui-monospace,SFMono-Regular,Menlo,monospace;color:#565656}.tool-actions{display:flex;gap:9px;flex-wrap:wrap;align-items:center;margin-top:13px}.tool-actions .primary,.tool-actions .quiet{font-size:10px;padding:9px 12px;min-height:35px;gap:8px}.tool-actions select{border:1px solid #dddddd;background:#fcfcfc;border-radius:5px;padding:8px;color:#636363;font-size:10px}.tool-output{margin-top:17px;min-height:70px;background:#f4f4f4;border:1px solid #e4e4e4;border-radius:7px;padding:14px;color:#696969;font-size:11px;line-height:1.7}.tool-output.error{background:#f5f5f5;border-color:#dadada;color:#6a6a6a}.tool-output pre{white-space:pre-wrap;font:15px/1.7 Georgia,serif;color:#606060;margin:8px 0 0}.tool-result-label{display:block;font-size:9px;letter-spacing:.8px;color:#8e8e8e}.tool-number{display:block;font:24px Georgia,serif;color:#636363;margin-top:5px}.vector-grid textarea{min-height:46px}.formula-card-list{display:grid;grid-template-columns:1fr 1fr;gap:10px;margin-top:17px}.formula-card-list article{background:#f4f4f4;border:1px solid #e4e4e4;border-radius:7px;padding:12px}.formula-card-list b{font-size:10px;color:#707070;font-weight:600}.formula-card-list p{font-size:9px!important;line-height:1.6!important;margin-top:6px!important}.formula-big{font:16px/1.4 Georgia,serif;color:#727272;margin-top:9px;overflow-wrap:anywhere}.saved-matrix-panel{display:flex;align-items:center;justify-content:space-between;gap:15px;flex-wrap:wrap;background:#f4f4f4;border:1px solid #e4e4e4;border-radius:7px;padding:12px 14px;margin:16px 0}.saved-label{font-size:8px;letter-spacing:1px;color:#8e8e8e;font-weight:600}.saved-matrix-panel p{font-size:10px;color:#8e8e8e;line-height:1.6;margin-top:4px}.saved-matrix-controls{display:flex;gap:7px;align-items:center;flex-wrap:wrap}.saved-matrix-controls input,.saved-matrix-controls select{border:1px solid #dadada;background:#ffffff;border-radius:5px;color:#616161;padding:8px;font-size:10px;max-width:170px}.saved-matrix-controls button{font-size:9px;padding:8px 10px}.focus-actions{display:flex;gap:9px;align-items:center;flex-wrap:wrap;margin-top:12px}.focus-actions .primary{margin-top:0}.history-card{margin-top:15px;padding:13px 15px;background:#fbfbfb;border:1px solid #e9e9e9;border-radius:7px}.history-card ul{list-style:none;padding:0;margin:8px 0 0}.history-card li{display:flex;justify-content:space-between;gap:10px;padding:6px 0;border-bottom:1px solid #f0f0f0;font-size:10px;color:#7a7a7a}.history-card li:last-child{border-bottom:0}.history-card small{color:#a2a2a2}.exam-result{display:flex;align-items:baseline;gap:10px;justify-content:center;margin:18px auto 4px;padding:11px 15px;background:#f1f1f1;border-radius:7px;max-width:280px}.exam-result span{font-size:9px;color:#7f7f7f}.exam-result strong{font:25px Georgia,serif;color:#666666}.exam-result small{font-size:9px;color:#969696}@media(max-width:700px){.tools-dialog{padding:22px 17px}.tool-grid,.formula-card-list{grid-template-columns:1fr}.tools-open{font-size:9px;padding:6px 8px}.tools-dialog h2{font-size:24px}.saved-matrix-panel{align-items:flex-start;flex-direction:column}.saved-matrix-controls{width:100%}.saved-matrix-controls input,.saved-matrix-controls select{max-width:none;flex:1;min-width:0}.progress-dialog{max-height:calc(100% - 28px);overflow:auto}}

/* The substituted right-hand-side column in Cramer's rule. */
.matrix-cell.cramer-column{background:var(--accent-soft,rgba(120,120,120,.16));border-radius:6px;box-shadow:inset 0 -2px currentColor;font-weight:700}