.course-main{max-width:1100px}.course-main .lesson-heading{margin-bottom:18px}.course-main .lesson-heading h1{font-size:34px}.course-main .lesson-heading p{font-size:16px}.course-goal{display:flex;align-items:start;gap:18px;justify-content:space-between;margin-bottom:22px}.course-goal details{flex:1;padding:14px 18px;border:1px solid #d7dff0;border-radius:10px;background:white;line-height:1.7}.course-goal summary{cursor:pointer;font-weight:600}.course-goal p{margin:10px 0 0}.duration{white-space:nowrap;font-size:14px;color:#63718b;padding-top:14px}.course-math{font:26px/1.85 Georgia,'Times New Roman',serif;background:#f5f7ff;border-radius:9px;padding:16px 20px;margin:18px 0;overflow-wrap:anywhere}.course-main .lesson-panel{line-height:1.7}.course-main .lesson-panel h3{line-height:1.6}.interactive-diagram{margin-top:24px}.slider-label{display:block;font-weight:600;margin-bottom:12px}.interactive-diagram input[type=range]{width:100%;accent-color:#213ee6}.visual-bar{display:grid;grid-template-columns:120px minmax(0,1fr) 65px;gap:12px;align-items:center;margin:22px 0;font-size:15px}.visual-bar>div{height:26px;background:#e1e7f3;border-radius:5px;overflow:hidden}.visual-bar i{display:block;height:100%;transition:width .2s;border-radius:5px}.visual-bar b{text-align:right}.number-pair{display:grid;grid-template-columns:1fr 1fr;gap:15px;margin-top:24px}.number-pair>div{padding:18px;border:1px solid #d6dff1;background:#fff;border-radius:9px}.number-pair small{display:block;font-size:14px;margin-bottom:10px}.number-pair strong{font:24px Georgia,serif}.combine-controls{display:flex;gap:20px;flex-wrap:wrap}.combine-controls label{display:flex;gap:15px;align-items:center}.combine-controls select{width:75px}.map-strip{margin-top:28px;width:var(--map-size);min-width:140px;background:#213ee6;color:#fff;border-radius:6px;padding:18px 10px;text-align:center}.area-figure{aspect-ratio:4/3;max-width:320px;margin:25px auto;background-color:#e9edff;background-image:linear-gradient(#8497f9 1px,transparent 1px),linear-gradient(90deg,#8497f9 1px,transparent 1px);background-size:25% 33.333%;border:1px solid #8497f9;display:grid;place-items:center}.area-figure span{padding:12px;background:#fffffff2;text-align:center;font:22px/1.6 Georgia,serif}.reveal-working{padding-left:28px}.reveal-working li{padding:10px 0 20px 10px;border-bottom:1px solid #e1e6f0;margin-bottom:18px}.reveal-working li::marker{font-weight:700;color:#213ee6}.reveal-working li>div{margin-top:10px}.supported-question{padding:22px 0;border-top:1px solid #e0e6f1}.course-fields{display:flex;gap:16px;flex-wrap:wrap;margin:18px 0}.course-fields label{font-size:14px;display:flex;flex-direction:column;gap:10px;max-width:100%;margin:0}.course-fields input{width:145px;font-size:21px}.course-main input:focus-visible{outline:3px solid #91a0ff;outline-offset:3px}.course-main h2:focus{outline:none}.chapter-section{margin-bottom:36px}.course-home .home-intro{margin-bottom:26px}.course-home .home-intro h1{font-size:40px}.course-home .home-intro p{line-height:1.7}.course-home .topic-formula{padding:18px 6px;margin:18px 0}.course-home .topic-card{padding:22px}.course-home .topic-meta{font-size:14px}.chapter-path{display:flex;gap:10px;flex-wrap:wrap;margin:20px 0}.chapter-path a{padding:10px 15px;border:1px solid #ccd5eb;border-radius:8px;background:white;color:#30415f;text-decoration:none;font-size:14px}.chapter-path a:hover{border-color:#213ee6}.review-grid{display:grid;grid-template-columns:1fr 1fr;gap:20px}.review-card{background:#fff;padding:22px;border-radius:12px;border:1px solid #dbe2f1;line-height:1.7}.review-card h2{font-size:20px;line-height:1.4}.review-card a{color:#213ee6}.review-card details{padding:12px 0;border-top:1px solid #e2e7f0}.review-card summary{cursor:pointer;font-weight:600}.review-grid .course-math{font-size:21px}.review-main h1{font-size:36px}.review-main>p{line-height:1.8}.course-home .tag{font-size:12px}@media(max-width:760px){.course-main .lesson-nav{grid-template-columns:repeat(3,minmax(0,1fr))}.course-main .lesson-nav button{font-size:14px;padding:10px 8px}.course-goal{display:block}.duration{display:block}.course-math{font-size:22px;padding:13px 12px}.visual-bar{grid-template-columns:82px minmax(0,1fr) 52px;gap:8px;font-size:14px}.number-pair{grid-template-columns:1fr}.course-main .lesson-panel{padding:22px 18px}.course-main .lesson-heading h1{font-size:29px}.course-fields{gap:12px}.course-fields input{width:126px}.course-fields label{flex:0 1 130px}.review-grid{grid-template-columns:1fr}.review-main{padding:26px 16px}.course-home .home-intro h1{font-size:32px}}@media(prefers-reduced-motion:reduce){.visual-bar i{transition:none}}@media print{.lesson-nav,.lesson-pagination,.button-group,form,.lesson-end,.chapter-path{display:none}.lesson-panel{border:0}.course-math{break-inside:avoid}}

.chapter-catalog{max-width:1100px;min-height:calc(100vh - 90px)}.chapter-catalog .home-intro{margin:8px 0 32px}.chapter-catalog .subtitle{line-height:1.8}.chapter-catalog-grid{display:grid;grid-template-columns:repeat(2,minmax(0,1fr));gap:24px}.chapter-entry{display:flex;flex-direction:column;padding:30px;background:white;border:1px solid #b8c4fc;border-radius:16px;text-decoration:none;color:inherit;transition:border-color .18s,box-shadow .18s}.chapter-entry:hover{border-color:#213ee6;box-shadow:0 10px 28px #213ee614}.chapter-entry-top{display:flex;justify-content:space-between;align-items:center;gap:12px;margin-bottom:28px}.chapter-entry-top .eyebrow{margin:0}.chapter-entry h2{font:800 28px/1.3 Manrope,Arial,sans-serif;margin:0 0 10px}.chapter-entry p{font-size:16px;line-height:1.8;color:#596b86;margin:14px 0}.chapter-entry .chapter-entry-zh{font-size:17px;margin:0}.chapter-entry-topics{display:flex;gap:8px;flex-wrap:wrap;margin:8px 0 28px}.chapter-entry-topics span{font-size:14px;background:#eff2ff;color:#344985;padding:7px 10px;border-radius:7px}.chapter-entry .topic-link{margin-top:auto}.catalog-note{font-size:14px;line-height:1.8;color:#68758f;margin-top:28px}.catalog-note span{display:block}@media(max-width:760px){.chapter-catalog-grid{grid-template-columns:1fr}.chapter-catalog{padding:28px 20px}.chapter-entry{padding:24px}.chapter-entry h2{font-size:25px}.chapter-catalog .subtitle span{display:block;padding:4px 0 0}}@media(prefers-reduced-motion:reduce){.chapter-entry{transition:none}}