:root{--seo-ink:#302740;--seo-muted:#51485f;--seo-lilac:#e6d9f1;--seo-border:#b8a2cc;--seo-mint:#dceee3;--seo-pink:#f6dfe5;--seo-cream:#fff3cb;--seo-paper:#fffaf0;--seo-plum:#65487c}
*{box-sizing:border-box}html{scroll-behavior:smooth;scroll-padding-top:22px}.seo-body{margin:0;background:linear-gradient(135deg,#f0e6f4,#fce9da 68%,#f7efd4);color:var(--seo-ink);font-family:'Trebuchet MS','Segoe UI',sans-serif;line-height:1.65;font-size:17px}.seo-body a{color:#56306e;text-underline-offset:3px}.seo-body a:hover{text-decoration-thickness:2px}.seo-body a:focus-visible,.seo-body summary:focus-visible{outline:3px solid #65487c;outline-offset:5px;border-radius:4px}.seo-skip{position:absolute;top:-100px;left:12px;z-index:5;padding:12px;background:var(--seo-cream)}.seo-skip:focus{top:12px}.seo-header{max-width:1280px;margin:auto;background:#e7dbf0;border-bottom:1px solid var(--seo-border);display:flex;justify-content:space-between;align-items:center;gap:30px;padding:20px 38px}.seo-brand{display:flex;align-items:center;gap:12px;font-size:30px;font-weight:800;line-height:1;text-decoration:none!important;color:var(--seo-ink)!important;flex-shrink:0}.seo-brand small{display:block;font-size:8px;letter-spacing:1.2px;margin-top:10px}.seo-header nav{display:flex;align-items:center;gap:28px;flex-wrap:wrap}.seo-header nav a{font-size:15px;font-weight:700;text-decoration:none}.seo-header nav a[aria-current]{background:#d7bfe8;padding:10px 16px;border-radius:14px}.seo-main{max-width:1120px;margin:0 auto;padding:28px 32px 70px}.seo-breadcrumb{display:flex;flex-wrap:wrap;align-items:center;gap:8px;font-size:13px;color:var(--seo-muted);margin:0 0 28px}.seo-breadcrumb a{color:var(--seo-muted)}.seo-page-intro{margin:0 0 30px}.seo-kicker{font-size:12px;text-transform:uppercase;letter-spacing:1.5px;font-weight:800;color:#654087;margin:0 0 12px}.seo-page-intro h1{font-size:clamp(30px,4.2vw,46px);line-height:1.2;max-width:950px;margin:10px 0 22px;letter-spacing:-1px}.seo-page-intro p:not(.seo-kicker){max-width:850px}.seo-lead{font-size:22px;font-weight:700;line-height:1.4}.seo-shared-note{font-size:15px;padding:14px 18px;background:var(--seo-mint);border:1px solid #9fbba9;border-radius:12px}.seo-class-links{display:flex;gap:12px;flex-wrap:wrap;margin:25px 0}.seo-class-links a{background:#f7effb;border:1px solid var(--seo-border);border-radius:15px;min-width:80px;padding:12px 16px;text-align:center;text-decoration:none;font-size:23px;font-weight:800}.seo-class-links a span{display:block;font-size:11px;font-weight:600}.seo-class-links a[aria-current]{color:white;background:var(--seo-plum)}.seo-action-row{display:flex;flex-wrap:wrap;align-items:center;gap:12px;margin:22px 0 4px}.seo-button{display:inline-flex;align-items:center;justify-content:center;gap:12px;min-height:48px;padding:12px 20px;background:#302740;border:1px solid #302740;color:white!important;border-radius:14px;font-size:15px;font-weight:800;text-decoration:none;line-height:1.45;text-align:center}.seo-button:hover{background:#65487c}.seo-button-soft{color:#302740!important;background:var(--seo-lilac);border-color:var(--seo-border)}.seo-button-soft:hover{background:#d8c4e9}.seo-how,.seo-toc,.seo-next{background:var(--seo-cream);border:1px solid #d8bd73;border-radius:22px;padding:25px 30px;margin:30px 0}.seo-how h2,.seo-toc h2,.seo-next h2{font-size:23px;line-height:1.3;margin:0 0 18px}.seo-how ol{padding-left:25px;margin:0}.seo-how li{margin:15px 0}.seo-grade-grid{display:grid;grid-template-columns:repeat(2,minmax(0,1fr));gap:24px}.seo-grade-card{position:relative;background:var(--seo-lilac);padding:28px;border:1px solid var(--seo-border);border-radius:24px;overflow:hidden}.seo-grade-card:nth-child(2n){background:var(--seo-mint);border-color:#99bfa8}.seo-grade-card:nth-child(3n){background:var(--seo-pink);border-color:#d9adba}.seo-grade-card h2{font-size:24px;line-height:1.35;margin:12px 0}.seo-class-number{font-family:var(--notebook-hand);font-size:36px;background:#fff8df;display:inline-flex;align-items:center;justify-content:center;min-width:62px;min-height:62px;border-radius:50%;border:2px dashed #9d7aaf;transform:rotate(-7deg)}.seo-small{font-size:14px;color:var(--seo-muted)}.seo-subject-nav{display:flex;flex-wrap:wrap;gap:10px;margin:30px 0}.seo-subject-nav a{padding:8px 14px;background:#fff5d7;border:1px solid #c5ad7b;border-radius:30px;text-decoration:none;font-size:14px;font-weight:700}.seo-subject-section{margin:42px 0}.seo-subject-section h2{font-size:28px;display:flex;gap:12px;align-items:center}.seo-subject-section h2 span{font-family:var(--notebook-hand);font-size:30px;min-width:48px;height:48px;display:inline-flex;justify-content:center;align-items:center;background:#dbeddf;border-radius:14px;transform:rotate(-5deg)}.seo-topic-grid{display:grid;grid-template-columns:repeat(2,minmax(0,1fr));gap:18px}.seo-topic-card{background:#f4ecfa;border:1px solid var(--seo-border);border-radius:20px;padding:22px}.seo-topic-card:nth-child(3n+2){background:#fcf0cb;border-color:#d6bd77}.seo-topic-card:nth-child(3n){background:#e3f0e4;border-color:#a1bca5}.seo-topic-card h3{font-size:21px;line-height:1.35;margin:0 0 12px}.seo-topic-card h3 a{color:#302740;text-decoration:none}.seo-topic-card p{font-size:15px;margin:12px 0}.seo-text-link{font-size:14px;font-weight:800}.seo-toc{background:#e7dcf1;border-color:var(--seo-border)}.seo-toc ol{display:grid;grid-template-columns:repeat(2,minmax(0,1fr));gap:12px 36px;padding-left:24px;margin-bottom:0}.seo-toc li{padding-left:2px}.seo-toc 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.seo-note-example{background:#ddecddaa;padding:10px 14px;border-radius:12px;font-size:22px}.seo-notes .seo-formula{display:table;background:#fff0bd;padding:9px 16px;border:1px solid #dab558;border-radius:11px;font-size:25px;font-weight:700}.seo-remember{background:#e6dcef;padding:16px 19px;border-radius:14px;border-left:5px solid #946cac;font-weight:700}.seo-visual{max-width:100%;overflow-x:auto;margin:20px auto;padding:6px 0}.seo-visual svg{display:block;width:100%;height:auto;max-width:470px;margin:0 auto}.seo-visual img{display:block;max-width:100%;height:auto}.seo-visual p{font-family:inherit;font-size:16px;color:var(--seo-ink)}.seo-notebook .decimal-column-example{max-width:100%;font-family:var(--notebook-hand)}.seo-drawing{max-width:420px!important;break-inside:avoid;margin:22px auto!important;background:#f9edd6aa!important}.seo-drawing svg{max-width:100%;height:auto}.seo-drawing figcaption{font-family:var(--notebook-hand);font-size:20px;color:#3d4b66;line-height:1.5}.seo-worked{padding:28px 30px;margin:30px 0;background:var(--seo-mint);border:1px solid #9ebfa9;border-radius:23px}.seo-worked h3{font-size:23px;line-height:1.45;margin:12px 0 20px}.seo-worked ol{padding-left:30px}.seo-worked li{padding-left:8px;margin:15px 0}.seo-worked li::marker{font-weight:800;color:#43634f}.seo-result{background:#fbf6dd;border:1px solid #d0bd85;border-radius:13px;padding:16px 18px;margin-bottom:0}.seo-help-grid{display:grid;grid-template-columns:repeat(2,minmax(0,1fr));gap:20px}.seo-help{background:var(--seo-cream);border-radius:18px;border:1px solid #d4ba79;padding:20px 24px}.seo-help-pink{background:var(--seo-pink);border-color:#d3aaba}.seo-help h3{font-size:19px;margin:0 0 12px}.seo-help p{margin:0;font-size:16px}.seo-vocabulary{margin:25px 0;background:#efe5f5;border:1px solid var(--seo-border);border-radius:17px;padding:17px 23px}.seo-vocabulary summary{cursor:pointer;font-weight:800}.seo-vocabulary dt{font-weight:800;margin-top:18px}.seo-vocabulary dd{margin-left:0}.seo-practice{margin:28px 0;background:#e5d8f0;border:1px solid #bba3cf;border-radius:22px;padding:24px 28px}.seo-practice h3{font-size:22px;margin:0 0 12px}.seo-practice p{margin:0;max-width:790px}.seo-concept{margin:26px 0;background:#fff1d1;padding:22px;border-radius:20px}.seo-concept figcaption{font-size:16px}.seo-next{background:#e3eddf;border-color:#a6b69b}.seo-next li{margin:12px 0}.seo-footer{display:flex;flex-wrap:wrap;gap:20px;justify-content:space-between;align-items:center;max-width:1120px;margin:auto;padding:25px 32px 40px;border-top:1px solid #cbb9d1;font-size:14px}.seo-footer>a:first-child{font-size:24px;font-weight:800;text-decoration:none}.seo-footer p{margin:0}
@media(max-width:760px){.seo-header{padding:20px 24px;align-items:flex-start;gap:20px;flex-wrap:wrap}.seo-header nav{gap:18px}.seo-main{padding:24px 23px 45px}.seo-topic-grid,.seo-grade-grid{grid-template-columns:1fr}.seo-page-intro h1{letter-spacing:-.6px}.seo-lead{font-size:20px}.seo-toc ol{grid-template-columns:1fr}.seo-notebook{padding:24px 24px 20px 36px;background-image:linear-gradient(to right,transparent 18px,#e8a6b5 18px,#e8a6b5 19px,transparent 19px),linear-gradient(#c8d4dc50 1px,transparent 1px),linear-gradient(90deg,#c8d4dc50 1px,transparent 1px)}.seo-notes{padding-left:18px}.seo-notes>li{padding-left:3px}.seo-notes p{font-size:22px}.seo-notes .seo-formula{font-size:23px;max-width:100%;overflow-wrap:anywhere}.seo-help-grid{grid-template-columns:1fr}.seo-lesson-part>h2{font-size:27px}.seo-worked,.seo-practice{padding:23px}.seo-how,.seo-toc,.seo-next{padding:23px}.seo-class-links{gap:9px}.seo-class-links a{min-width:64px;padding:10px 13px}.seo-class-links a span{font-size:10px}.seo-action-row{align-items:stretch}.seo-button{max-width:100%}.seo-footer{padding:24px}.seo-breadcrumb{font-size:12px}.seo-subject-nav a{font-size:13px}.seo-visual .decimal-column-table{font-size:22px}}
@media(max-width:400px){.seo-main{padding:20px 16px 40px}.seo-header{padding:18px 16px}.seo-brand{font-size:28px}.seo-header nav{gap:14px}.seo-header nav a{font-size:13px}.seo-class-links a{min-width:54px;padding:8px 10px}.seo-class-links a span{max-width:40px;font-size:9px}.seo-notebook{padding-right:17px}.seo-notes p{font-size:21px}.seo-note-example{overflow-wrap:anywhere}.seo-worked{padding:20px 18px}.seo-action-row .seo-button{width:100%}}
@media(prefers-reduced-motion:reduce){html{scroll-behavior:auto}}
@media print{.seo-header,.seo-footer,.seo-practice,.seo-action-row,.seo-class-links,.seo-toc,.seo-breadcrumb{display:none!important}.seo-body{background:white;color:#111}.seo-main{max-width:none;padding:0}.seo-notebook,.seo-worked,.seo-help{box-shadow:none;border-color:#999;background:white}.seo-notes p{font-family:'Trebuchet MS',sans-serif;font-size:14pt}.seo-lesson-part{break-before:page}.seo-lesson-part:first-of-type{break-before:auto}.seo-drawing,.seo-worked{break-inside:avoid}}