:root{--bg-main: #f5f7fb;--bg-sidebar: #0f172a;--bg-panel: #ffffff;--bg-panel-muted: #eef2f8;--text-primary: #0f172a;--text-secondary: #475569;--text-muted: #64748b;--text-inverse: #f8fafc;--text-on-accent: #ffffff;--accent: #2563eb;--accent-strong: #1d4ed8;--border-soft: rgba(15, 23, 42, .08);--border-contrast: rgba(148, 163, 184, .25);--shadow-soft: 0 24px 60px -40px rgba(15, 23, 42, .35);--sidebar-item-bg: rgba(148, 163, 184, .15);--sidebar-item-hover: rgba(148, 163, 184, .25);--sidebar-item-active: #2563eb;--sidebar-badge-bg: rgba(15, 23, 42, .55);--scrollbar-thumb: rgba(148, 163, 184, .45);--font-base: "Inter", system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", sans-serif;font-family:var(--font-base);line-height:1.5;font-weight:400;color:var(--text-primary);background-color:var(--bg-main)}[data-theme=dark]{--bg-main: #0b1221;--bg-sidebar: #050914;--bg-panel: #111a2f;--bg-panel-muted: #0f1628;--text-primary: #f8fafc;--text-secondary: #cbd5f5;--text-muted: #9faad5;--text-inverse: #f8fafc;--text-on-accent: #ffffff;--accent: #3b82f6;--accent-strong: #60a5fa;--border-soft: rgba(148, 163, 184, .2);--border-contrast: rgba(30, 41, 59, .6);--shadow-soft: 0 24px 60px -44px rgba(8, 12, 24, .85);--sidebar-item-bg: rgba(30, 41, 59, .6);--sidebar-item-hover: rgba(37, 56, 88, .75);--sidebar-item-active: #3b82f6;--sidebar-badge-bg: rgba(148, 163, 184, .35);--scrollbar-thumb: rgba(148, 163, 184, .35)}*,*:before,*:after{box-sizing:border-box}html{height:100%}body{margin:0;min-height:100%;background:var(--bg-main);color:var(--text-primary);overflow:hidden}#root{min-height:100vh;height:100%}.centered{display:grid;place-items:center;min-height:100vh;padding:2rem;background:var(--bg-main)}.card{width:min(420px,100%);background:var(--bg-panel);border-radius:16px;padding:2rem;box-shadow:var(--shadow-soft);border:1px solid var(--border-soft);color:var(--text-primary);text-align:center}button{cursor:pointer;border:none;border-radius:999px;padding:.75rem 1.5rem;background:var(--accent);color:var(--text-on-accent);font-size:1rem;font-weight:600;transition:transform .15s ease,box-shadow .15s ease,background .2s ease;box-shadow:0 14px 35px -20px #2563eba6}.primary-button{min-width:160px;justify-content:center}.btn-success{background:#16a34a;box-shadow:0 16px 32px -20px #16a34a99}.btn-success:hover{background:#22c55e;box-shadow:0 18px 36px -20px #22c55e99}.btn-error{background:#dc2626;box-shadow:0 18px 36px -20px #dc262699}.btn-error:hover{background:#ef4444}.btn-saving{position:relative;padding-right:2.75rem}.btn-saving:after{content:"";position:absolute;top:50%;right:1.2rem;width:14px;height:14px;border-radius:50%;border:2px solid rgba(255,255,255,.45);border-top-color:#fff;transform:translateY(-50%);animation:buttonSpin .8s linear infinite}@keyframes buttonSpin{to{transform:translateY(-50%) rotate(360deg)}}button:hover{transform:translateY(-1px);background:var(--accent-strong);box-shadow:0 20px 40px -18px #2563eb80}.error{margin-top:1rem;color:#b91c1c}.app-shell{min-height:100vh;display:flex;flex-direction:column;background:var(--bg-main)}.app-header{display:flex;justify-content:space-between;align-items:center;padding:1.5rem 2.5rem;background:var(--bg-panel);border-bottom:1px solid var(--border-soft);gap:1.5rem}.app-header h1{margin:0;color:var(--text-primary)}.app-header p{margin:.25rem 0 0;color:var(--text-secondary)}.header-actions{display:flex;align-items:center;gap:1rem}.app-content{flex:1;padding:2rem;max-width:1200px;width:min(100%,1200px);margin:0 auto;color:var(--text-primary)}.course-shell{display:grid;grid-template-columns:320px 1fr;height:100vh;background:var(--bg-main);overflow:hidden}.course-shell>.sidebar,.course-shell>.lesson-area{min-height:0}.sidebar{background:var(--bg-sidebar);color:var(--text-inverse);padding:2rem 1.5rem;display:flex;flex-direction:column;gap:1.5rem;overflow-y:auto;border-right:1px solid 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