.sudoku-lesson{font-size:1.0625rem;line-height:1.8;color:#183333}
.sudoku-lesson [hidden]{display:none!important}
.sudoku-lesson h2{scroll-margin-top:6rem}
.sudoku-lesson .lesson-byline{font-size:.875rem;color:#526765;margin:0 0 1.5rem}
.lesson-index{display:flex;flex-wrap:wrap;gap:.75rem 1.2rem;margin:1.5rem 0 2.5rem;padding:1.2rem;border:1px solid #b9c5c2;border-radius:1rem;font-size:1rem;line-height:1.5}
.sudoku-lesson .lesson-figure{max-width:560px;margin:2rem auto 1.5rem}
.lesson-figure img{display:block;width:100%;height:auto;border:1px solid #b9c5c2;border-radius:.75rem}
.sudoku-lesson figcaption{font-size:.9375rem;line-height:1.6;color:#36514f;margin:.8rem 0 0;text-align:left}
.lesson-walk{margin:2rem 0;padding:1.25rem;background:#f3efe5;border:1px solid #a2b1ac;border-radius:1rem}
.lesson-controls{display:flex;flex-wrap:wrap;gap:.6rem;margin-bottom:1.5rem}
.lesson-controls button{min-height:44px;padding:.65rem .9rem;border:1px solid #183333;border-radius:1.5rem;background:#fffdf7;color:#183333;font-family:inherit;font-weight:700;font-size:.9375rem;line-height:1.4;cursor:pointer}
.lesson-controls [data-lesson-next]{background:#183333;color:#fffdf7}
.lesson-controls button:disabled{opacity:.45;cursor:default}
.lesson-controls button:focus-visible,.lesson-detail summary:focus-visible,.lesson-index a:focus-visible{outline:3px solid #ad472f;outline-offset:4px}
.lesson-layout{display:grid;gap:1.5rem;align-items:start}
.sudoku-lesson .lesson-board{border-collapse:collapse;table-layout:fixed;width:100%;max-width:520px;margin:0 auto;font-size:1.125rem;line-height:1.2;text-align:center;font-variant-numeric:tabular-nums}
.lesson-board td,.lesson-board th{padding:0!important;text-align:center;vertical-align:middle;border:0}
.lesson-board thead td,.lesson-board th{height:1.6rem;background:transparent;font-size:.875rem;font-weight:500;color:#526765}
.lesson-board thead td,.lesson-board tbody th{width:1.4rem}
.lesson-board tbody td{height:2.3rem;background:#fffdf7;border:1px solid #899c98;font-weight:800}
.lesson-board tbody td:nth-child(2){border-left:3px solid #183333}
.lesson-board tbody td:nth-child(3n+1){border-right:3px solid #183333}
.lesson-board tbody tr:nth-child(3n) td{border-bottom:3px solid #183333}
.lesson-board tbody tr:first-child td{border-top:3px solid #183333}
.lesson-board tbody td.lesson-related{background:#e0eae4}
.lesson-board tbody td.lesson-target{background:#f4bd4f;outline:3px solid #183333;outline-offset:-4px}
.lesson-board .lesson-added{text-decoration:underline;text-underline-offset:3px}
.lesson-explanation h3{font-size:1.15rem;line-height:1.4;letter-spacing:-.02em;margin:.4rem 0 .8rem}
.lesson-explanation p{font-size:1rem;line-height:1.7;margin:0}
.lesson-explanation .lesson-step{font-weight:800;font-size:.875rem;color:#79402c}
.sudoku-lesson .lesson-key{font-size:.875rem;line-height:1.6;margin:1.2rem 0 0;color:#36514f}
.lesson-detail{margin:1.2rem 0;border:1px solid #b9c5c2;border-radius:.75rem;padding:1rem}
.lesson-detail summary{font-weight:700;cursor:pointer;line-height:1.6;min-height:44px}
.lesson-detail[open] summary{margin-bottom:1.5rem}
.sudoku-lesson .lesson-transcript{padding-left:1.5rem}
.lesson-transcript li{margin:1.5rem 0}
.lesson-transcript li p{margin:.6rem 0;font-size:1rem}
.lesson-links{display:flex;flex-wrap:wrap;gap:1rem;margin-top:2rem;align-items:center}
.lesson-links a:first-child{display:inline-flex;align-items:center;min-height:48px;background:#183333;color:#fffdf7;border-radius:2rem;padding:.75rem 1.2rem;text-decoration:none;font-weight:800}
.lesson-page main>section>div{padding-top:2rem;padding-bottom:2rem}
.lesson-page main>article>.prose-puzzle{padding-top:2rem}
@media(max-width:639px){.lesson-page h1{font-size:2.25rem;line-height:1.08}.lesson-page main>section>div>p:last-child{font-size:1rem;line-height:1.6}}
@media(min-width:900px){.lesson-layout{grid-template-columns:1.25fr 1fr}.lesson-board tbody td{height:2.5rem}}
@media(max-width:420px){.lesson-walk{padding:1rem .6rem}.lesson-board tbody td{height:1.95rem;font-size:1rem}.lesson-controls{gap:.5rem}.lesson-controls button{font-size:.875rem}.lesson-controls [data-lesson-next]{flex:1}.lesson-detail{padding:.8rem}}