:root{--paper:#f5f3ed;--ink:#25352f;--quiet:#6d756e;--green:#295e47;--line:#d8dcd3;--light:#eee6d4;--dark:#94aa92;--mark:#e0c56c;font-family:Arial,Helvetica,sans-serif;color:var(--ink);background:var(--paper);font-synthesis:none}
*{box-sizing:border-box}body{margin:0}button,select{font:inherit;color:inherit}button,a,select{-webkit-tap-highlight-color:transparent}button{cursor:pointer}a{color:inherit}button:focus-visible,a:focus-visible,select:focus-visible,summary:focus-visible{outline:3px solid #b57928;outline-offset:3px}button{border:0;background:none}button:disabled{opacity:.32;cursor:default}button,select{min-height:44px}button[hidden],[hidden]{display:none!important}.site-header{height:65px;display:flex;align-items:center;justify-content:space-between;max-width:1240px;margin:auto;padding:0 18px;border-bottom:1px solid var(--line)}.brand{font:26px Georgia,'Times New Roman',serif;text-decoration:none;letter-spacing:-.6px}.brand span{font:12px Arial,sans-serif;letter-spacing:1px;margin-left:9px;border-left:1px solid #b8c1b7;padding-left:12px;vertical-align:middle}.download{font-size:12px;text-decoration:none;min-height:44px;display:flex;align-items:center;gap:9px}.download span{font-size:20px}main{max-width:1240px;margin:0 auto;padding:0 16px}.toolbar{display:flex;gap:10px;justify-content:space-between;align-items:center;padding:12px 0}.modes{display:flex;background:#e7eae2;padding:3px;border-radius:6px;flex-shrink:0}.modes button{font-size:12px;min-height:44px;padding:0 12px;border-radius:4px;transition:background .15s,color .15s}.modes button[aria-pressed=true]{background:var(--green);color:white}.chapter-label{min-width:0;max-width:52%}.chapter-label select{border:0;border-bottom:1px solid var(--line);background:transparent;font-size:12px;max-width:100%;width:100%;padding:0 20px 0 2px;text-overflow:ellipsis}.workspace{display:grid;gap:20px}.board-column{min-width:0}.position-heading{display:flex;justify-content:space-between;align-items:center;min-height:32px;font-size:12px}.quiet{color:var(--quiet);font-variant-numeric:tabular-nums}.board-wrap{position:relative;aspect-ratio:1;max-width:100%;border:1px solid #6f856d}.board{display:grid;grid-template-columns:repeat(8,1fr);aspect-ratio:1;user-select:none;-webkit-user-select:none}.square{position:relative;display:grid;place-items:center;aspect-ratio:1;min-height:0;padding:0;border-radius:0;background:var(--light);touch-action:manipulation}.square.dark{background:var(--dark)}.square img{width:88%;height:88%;object-fit:contain;pointer-events:none;z-index:2;transition:transform .14s}.square.last{box-shadow:inset 0 0 0 100px #e0c56c52}.square.selected{box-shadow:inset 0 0 0 100px #e5bc3880}.square.selected img{transform:translateY(-2px)}.square.target:after{content:'';width:25%;height:25%;background:#294e4260;border-radius:50%;position:absolute;z-index:3}.square.target.occupied:after{width:86%;height:86%;background:none;border:4px solid #294e4270}.square:focus-visible{outline:3px solid #a66d18;outline-offset:-3px;z-index:3}.coordinate{position:absolute;font-size:9px;line-height:1;font-weight:bold;z-index:4;pointer-events:none;color:#47603e}.square.dark .coordinate{color:#fcfcf2}.rank{top:3px;left:3px}.file{bottom:3px;right:3px}.board-arrow{position:absolute;inset:0;pointer-events:none;width:100%;height:100%}.board-controls{display:flex;align-items:center;justify-content:space-between;border-bottom:1px solid var(--line);height:49px;gap:8px}.move-controls{display:flex}.move-controls button{width:42px;font-size:24px;line-height:1}.current-move{font-size:13px;font-variant-numeric:tabular-nums;margin-left:auto;white-space:nowrap}.flip{font-size:24px;width:44px}.board-help{font-size:11px;color:var(--quiet);margin:7px 0 0;min-height:14px}.lesson-column{min-width:0;padding-bottom:4px}.eyebrow{font-size:11px;letter-spacing:1.2px;color:var(--green);margin:0 0 9px;text-transform:none}h1{font:28px/1.17 Georgia,'Times New Roman',serif;letter-spacing:-.4px;margin:0 0 9px;max-width:22ch}.game-label{font-size:12px;line-height:1.6;color:var(--quiet);margin:0 0 20px}.goal,.question{font-size:15px;line-height:1.65;margin:0 0 19px}.line-choices{display:flex;flex-wrap:wrap;gap:5px;margin:0 0 10px}.line-choices:empty{display:none}.line-choices button{font-size:11px;border-bottom:2px solid transparent;padding:4px 9px;min-height:36px}.line-choices button[aria-pressed=true]{color:var(--green);border-color:var(--green)}.move-list{display:flex;flex-wrap:wrap;gap:4px;margin-bottom:16px;max-height:126px;overflow:auto;scrollbar-width:thin;align-content:start}.move-list button{min-height:34px;padding:6px 8px;font-size:13px;border-radius:3px;background:#e8ece4}.move-list button[aria-current=true]{background:var(--green);color:#fff}.move-list .move-num{opacity:.65;font-size:10px;margin-right:4px}.comment{font-size:15px;line-height:1.75;margin:0 0 22px;min-height:52px;animation:reveal .18s ease-out}.takeaway{border-top:1px solid var(--line);padding:16px 0 0}.takeaway>span{font-size:10px;letter-spacing:1px;color:var(--green)}.takeaway p{font-size:14px;line-height:1.65;margin:7px 0 0}.section-navigation{display:flex;justify-content:space-between;gap:10px;border-top:1px solid var(--line);padding-top:10px;margin-top:24px}.text-button{padding:0;font-size:12px;color:var(--green);text-align:left}.text-button:hover{text-decoration:underline}.solid-button{background:var(--green);color:white;padding:10px 16px;border-radius:4px;font-size:12px}.practice-actions{display:flex;gap:18px;align-items:center;flex-wrap:wrap;margin:20px 0}.question{font-size:18px;font-family:Georgia,'Times New Roman',serif;line-height:1.5}.feedback{font-size:14px;line-height:1.6;margin:12px 0}.feedback:empty{display:none}.feedback.correct{color:var(--green);font-weight:bold}.hint{font-size:13px;line-height:1.65;border-left:2px solid #a6b49a;padding-left:12px;animation:reveal .18s ease-out}.sources{border-top:1px solid var(--line);margin:34px 0 28px;padding-top:14px;font-size:12px;line-height:1.7;color:var(--quiet)}.sources summary{cursor:pointer;padding:6px 0;min-height:36px}.source-content{max-width:760px;padding:8px 0}.source-content ul{padding-left:18px}.source-content li{margin:8px 0}.source-content a{text-underline-offset:3px}.license{font-size:11px}.sr-only{position:absolute;width:1px;height:1px;overflow:hidden;clip:rect(0,0,0,0);white-space:nowrap}.noscript{padding:24px}.error{padding:40px 0;line-height:1.7}@keyframes reveal{from{opacity:.4;transform:translateY(3px)}to{opacity:1;transform:none}}
@media(min-width:760px){.site-header{height:83px;padding:0 32px}.brand{font-size:33px}.download{font-size:13px}main{padding:0 32px}.toolbar{padding:23px 0 16px}.modes button{font-size:13px;padding:0 20px;min-height:38px}.chapter-label{width:350px;max-width:52%}.chapter-label select{font-size:13px}.workspace{grid-template-columns:minmax(350px,1.35fr) minmax(290px,1fr);gap:45px;align-items:start}.board-column{max-width:640px}.lesson-column{padding:37px 0 0}h1{font-size:35px}.game-label{margin-bottom:25px}.position-heading{height:37px}.board-help{font-size:12px}.move-controls button{width:46px}.current-move{font-size:14px}.coordinate{font-size:11px}.sources{margin-top:46px}.comment,.goal{font-size:16px}}
@media(min-width:1050px){.workspace{grid-template-columns:minmax(400px,620px) minmax(320px,1fr);gap:58px}h1{font-size:39px}.lesson-column{max-width:450px}}
@media(max-width:359px){main{padding:0 12px}.site-header{padding:0 12px;height:55px}.brand{font-size:24px}.modes button{padding:0 9px;font-size:11px}.toolbar{gap:7px;padding:8px 0}.chapter-label select{font-size:11px}.workspace{gap:16px}h1{font-size:26px}.download{font-size:11px}.board-help{font-size:10px}.move-controls button{width:36px}}
.mobile-prompt{font-size:15px;line-height:1.45;margin:2px 0 8px;font-weight:600}
@media(max-width:759px){.lesson-column h1,.lesson-column .eyebrow,.practice-panel .question{display:none}.game-label{margin:0 0 14px}.workspace{gap:15px}}
@media(min-width:760px){.mobile-prompt{display:none}}
.lesson-text{animation:reveal .18s ease-out}.square.last.occupied img{animation:reveal .16s ease-out}
@media(prefers-reduced-motion:reduce){*,*:before,*:after{animation:none!important;transition:none!important;scroll-behavior:auto!important}}

.mobile-practice-actions{display:none;gap:12px}.mobile-practice-actions button{min-width:44px;font-size:12px;padding:0;color:var(--green)}
@media(max-width:759px){.mobile-practice-actions{display:flex}.move-controls.practice-unrevealed{display:none}.board-help{line-height:1.5}.practice-panel .hint{display:none}}