.textbook-hub {padding-bottom:48px;}
.textbook-hub > section {margin-block:32px;}
.textbook-hub .page-intro {margin-top:32px;}
.textbook-grid {display:grid;grid-template-columns:repeat(2,minmax(0,1fr));gap:24px;}
.textbook-grid .card {display:flex;flex-direction:column;gap:16px;padding:28px;}
.textbook-grid h2 {font-size:28px;}
.textbook-grid p {color:var(--muted);}
.textbook-grid strong {margin-top:auto;}
.textbook-back {display:inline-block;margin-bottom:16px;}
.textbook-chapter {margin-bottom:20px;}
.geometry-lesson {margin:0;}
.geometry-lesson > .shell > section {margin-block:0;}
.geometry-lesson .lesson-heading h1 {font-size:clamp(32px,5vw,46px);}
@media(max-width:700px){.textbook-grid {grid-template-columns:1fr;gap:16px;}.textbook-grid .card {padding:22px;}.textbook-grid h2 {font-size:25px;}}
.textbook-index {display:grid;grid-template-columns:repeat(2,minmax(0,1fr));gap:36px 64px;padding-top:32px;}
.textbook-index > section {margin:0;min-width:0;}
.textbook-index .page-intro {grid-column:1/-1;margin:0;padding:0;}
.textbook-index .page-intro h1 {max-width:none;font-size:clamp(32px,4vw,46px);margin:0;}
.textbook-index .textbook-chapter {margin-bottom:10px;}
.textbook-index .textbook-chapter h2 {font-size:26px;line-height:1.3;margin:0;}
.textbook-topics {list-style:none;padding:0;margin:0;}
.textbook-topics li {margin:0;padding:0;border-bottom:1px solid var(--line);}
.textbook-topics a {display:flex;align-items:center;justify-content:space-between;gap:18px;min-height:52px;padding:11px 4px;font-size:18px;font-weight:600;line-height:1.5;color:var(--ink);text-decoration:none;transition:color .15s,background-color .15s;}
.textbook-topics a::after {content:'→';flex:none;font-size:21px;font-weight:400;color:var(--accent);}
.textbook-topics a:hover {color:var(--accent);background-color:#eef4f0;text-decoration:none;}
.textbook-topics a:focus-visible {outline:2px solid var(--accent);outline-offset:4px;border-radius:2px;}
@media(max-width:700px){.textbook-index{grid-template-columns:1fr;gap:28px;padding-top:24px;}.textbook-index .textbook-chapter h2{font-size:24px;}}