:root{--bg:#030304;--panel:#101114;--raised:#17181c;--line:#2b2d33;--text:#f4f5f7;--copy:#bec2cb;--muted:#838894;--amber:#f59e0b;--amber2:#fbbf24;--green:#34d399}*{box-sizing:border-box}html,body{margin:0;width:100%;height:100%;overflow:hidden;background:var(--bg);color:var(--text);font:14px/1.5 Inter,ui-sans-serif,system-ui,-apple-system,"Segoe UI",sans-serif}button,input,textarea{font:inherit}.lesson-app{height:100vh;display:grid;grid-template-rows:68px minmax(0,1fr);background:radial-gradient(circle at 44% -10%,rgba(245,158,11,.06),transparent 30rem),#030304}.lesson-topbar{z-index:10;display:flex;align-items:center;gap:16px;padding:0 18px;border-bottom:1px solid #27292e;background:rgba(7,8,9,.96);box-shadow:0 8px 30px rgba(0,0,0,.25)}.lesson-back,.lesson-topbar button{display:grid;place-items:center;min-height:36px;padding:0 12px;border:1px solid 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