:root {
    --bg: #0b1120; --surface: #1a2332; --text: #f1f7fc;
    --accent: #34d399; --accent-rgb: 52, 211, 153;
    --border: #2a3a4e; --success: #10b981;
    --warning: #f59e0b; --error: #ef4444;
    --teal: #14b8a6; --sky: #38bdf8; --cyan: #22d3ee;
    --code-bg: #0a0f18;
    --glow: rgba(52,211,153,0.15); --radius: 12px;
}
[data-theme="light"] {
    --bg: #f0f4f8; --surface: #ffffff; --text: #1a2332;
    --border: #d1d9e6; --code-bg: #f8fafc;
    --glow: rgba(52,211,153,0.08);
}
* { margin: 0; padding: 0; box-sizing: border-box; }
::selection { background: var(--accent); color: #000; }
::-webkit-scrollbar { width: 6px; height: 6px; }
::-webkit-scrollbar-track { background: var(--bg); }
::-webkit-scrollbar-thumb { background: var(--border); border-radius: 3px; }
::-webkit-scrollbar-thumb:hover { background: var(--accent); }
html { scroll-behavior: smooth; }
body {
    font-family: 'Inter', system-ui, -apple-system, sans-serif;
    background: var(--bg); color: var(--text); min-height: 100vh;
    padding: 1rem; display: flex; flex-direction: column; align-items: center;
    line-height: 1.6;
}
.topnav {
    width: 100%; max-width: 1100px;
    background: var(--surface); border: 1px solid var(--border);
    padding: 0.6rem 1rem; display: flex; gap: 0.5rem; align-items: center;
    border-radius: var(--radius); margin-bottom: 1.5rem; flex-wrap: wrap;
    box-shadow: 0 4px 24px var(--glow);
    backdrop-filter: blur(12px);
}
.topnav .brand {
    font-weight: 700; color: var(--text); margin-right: auto; font-size: 0.9rem;
    background: linear-gradient(135deg, var(--accent), var(--teal));
    -webkit-background-clip: text; -webkit-text-fill-color: transparent;
}
.topnav a {
    color: #8899aa; text-decoration: none; font-size: 0.8rem;
    padding: 0.3rem 0.7rem; border-radius: 6px; transition: all 0.25s;
    font-weight: 500;
}
.topnav a:hover { color: white; background: rgba(255,255,255,0.08); transform: translateY(-1px); }
.topnav a.active { color: var(--accent); background: rgba(var(--accent-rgb),0.12); box-shadow: 0 0 12px var(--glow); }
.topnav .beuvault-link { color: var(--accent); font-weight: 600; font-size: 0.75rem; letter-spacing: 0.02em; margin-right: 0.25rem; }
.topnav .beuvault-link:hover { color: #6ee7b7; background: rgba(var(--accent-rgb),0.1); }
.container { width: 100%; max-width: 1000px; }
.header { text-align: center; padding: 1rem 0 1.5rem; margin-bottom: 2rem; position: relative; }
.header::after {
    content: ''; position: absolute; bottom: 0; left: 20%; right: 20%;
    height: 2px; background: linear-gradient(90deg, transparent, var(--accent), transparent);
    border-radius: 1px;
}
.header h1 {
    font-size: 2rem; font-weight: 800; letter-spacing: -0.03em;
    background: linear-gradient(135deg, var(--accent), var(--teal), var(--sky));
    -webkit-background-clip: text; -webkit-text-fill-color: transparent;
    background-size: 200% 200%; animation: gradShift 6s ease infinite;
}
@keyframes gradShift { 0%,100% { background-position: 0% 50%; } 50% { background-position: 100% 50%; } }
.lesson-step { display: none; }
.lesson-step.active { display: block; }
.step-nav {
    display: flex; align-items: center; justify-content: space-between;
    gap: 0.75rem; margin: 1.5rem 0; padding: 0.85rem 1rem;
    background: var(--surface); border: 1px solid var(--border);
    border-radius: var(--radius); flex-wrap: wrap;
    position: sticky; top: 0; z-index: 50;
    backdrop-filter: blur(8px);
    box-shadow: 0 4px 20px rgba(0,0,0,0.3);
}
.step-nav .step-info { font-size: 0.8rem; color: #94a3b8; white-space: nowrap; }
.step-nav .step-info strong { color: var(--accent); }
.step-btns { display: flex; gap: 0.5rem; }
.step-btn {
    padding: 0.5rem 1.2rem; background: var(--bg); border: 1px solid var(--border);
    color: var(--text); border-radius: 8px; cursor: pointer; font-weight: 600;
    font-size: 0.8rem; transition: all 0.2s;
    min-height: 44px;
}
.step-btn:hover { border-color: var(--accent); color: var(--accent); }
.step-btn:disabled { opacity: 0.4; cursor: default; border-color: var(--border); color: #475569; }
.step-btn.primary { background: var(--accent); color: #000; border-color: var(--accent); }
.step-btn.primary:hover { background: #6ee7b7; }
.step-progress {
    display: flex; gap: 0.35rem; align-items: center; flex: 1; justify-content: center;
}
.step-dot {
    width: 10px; height: 10px; border-radius: 50%;
    background: var(--border); transition: all 0.3s; cursor: pointer;
    flex-shrink: 0;
}
.step-dot.active { background: var(--accent); box-shadow: 0 0 8px var(--glow); }
.step-dot.done { background: var(--accent); opacity: 0.5; }
.step-dot:hover { transform: scale(1.3); }
@media (max-width: 640px) {
    .step-nav { flex-direction: column; gap: 0.5rem; padding: 0.6rem; }
    .step-btns { width: 100%; }
    .step-btn { flex: 1; text-align: center; padding: 0.4rem 0.8rem; font-size: 0.75rem; }
    .step-progress { order: -1; }
    .step-info { font-size: 0.7rem; }
    #stepTitle { max-width: 100% !important; }
}
.section {
    background: var(--surface); border: 1px solid var(--border);
    border-radius: var(--radius); padding: 2rem; margin: 2rem 0;
    transition: box-shadow 0.3s;
}
.section:hover { box-shadow: 0 8px 32px var(--glow); }
.section h2 {
    color: var(--accent); font-size: 1.3rem; font-weight: 700;
    border-bottom: 1px solid var(--border); padding-bottom: 0.75rem; margin-bottom: 1.25rem;
    display: flex; align-items: center; gap: 0.5rem;
}
.section h3 { color: #cbd5e1; margin: 1rem 0 0.5rem; font-weight: 600; }
.advanced-toggle {
    display: inline-flex; align-items: center; gap: 0.4rem;
    background: rgba(var(--accent-rgb),0.08); border: 1px solid rgba(var(--accent-rgb),0.2);
    color: var(--accent); padding: 0.4rem 0.9rem; border-radius: 999px;
    font-size: 0.75rem; font-weight: 600; cursor: pointer; transition: all 0.2s;
    margin: 0.5rem 0; letter-spacing: 0.02em;
}
.advanced-toggle:hover { background: rgba(var(--accent-rgb),0.15); transform: translateY(-1px); }
.advanced-toggle .arrow { display: inline-block; transition: transform 0.3s; font-size: 0.65rem; }
.advanced-toggle.open .arrow { transform: rotate(90deg); }
.advanced-content {
    max-height: 0; overflow: hidden;
    transition: max-height 0.4s ease, opacity 0.3s ease, margin 0.3s ease;
    opacity: 0; margin: 0;
}
.advanced-content.open { max-height: 2000px; opacity: 1; margin: 1rem 0; }
.advanced-content > .theory-box { border-left-color: var(--teal); }
.objectives-toggle {
    margin: 0.75rem 0 0; text-align: left;
    background: rgba(0,0,0,0.25); border-radius: 0 var(--radius) var(--radius) 0;
    border-left: 4px solid var(--accent); backdrop-filter: blur(4px);
}
.objectives-toggle .obj-btn {
    display: flex; align-items: center; gap: 0.4rem; width: 100%; text-align: left;
    background: none; border: none; color: var(--accent); cursor: pointer;
    padding: 0.5rem 1rem; font-size: 0.82rem; font-weight: 600; transition: all 0.2s;
    border-radius: 0 var(--radius) 0 0; letter-spacing: 0.01em;
}
.objectives-toggle .obj-btn:hover { background: rgba(var(--accent-rgb),0.08); }
.objectives-toggle .obj-btn .arrow { display: inline-block; transition: transform 0.3s; font-size: 0.6rem; }
.objectives-toggle .obj-btn.open .arrow { transform: rotate(90deg); }
.objectives-toggle .obj-content {
    max-height: 0; overflow: hidden;
    transition: max-height 0.3s ease, opacity 0.2s ease, padding 0.2s ease;
    opacity: 0; padding: 0 1rem;
}
.objectives-toggle .obj-content.open { max-height: 500px; opacity: 1; padding: 0 1rem 0.75rem; }
.objectives-toggle .obj-content ul { margin: 0; padding-left: 1.25rem; }
.objectives-toggle .obj-content li { font-size: 0.82rem; color: #94a3b8; margin-bottom: 0.3rem; line-height: 1.5; }
.code-reveal-btn {
    display: inline-flex; align-items: center; gap: 0.4rem;
    background: var(--code-bg); border: 1px solid var(--border);
    color: var(--accent); padding: 0.35rem 0.85rem; border-radius: 6px;
    font-size: 0.75rem; font-weight: 600; cursor: pointer; font-family: 'JetBrains Mono', monospace;
    transition: all 0.2s; margin: 0.5rem 0;
    min-height: 44px;
}
.code-reveal-btn:hover { border-color: var(--accent); background: rgba(var(--accent-rgb),0.08); }
.code-reveal-btn .arrow { display: inline-block; transition: transform 0.3s; font-size: 0.6rem; }
.code-reveal-btn.open .arrow { transform: rotate(90deg); }
.code-block {
    max-height: 0; overflow: hidden;
    transition: max-height 0.35s ease, opacity 0.25s ease, margin 0.25s ease;
    opacity: 0; margin: 0;
}
.code-block.open { max-height: 2000px; opacity: 1; margin: 0.75rem 0; }
.code-block pre { margin: 0; }
.code-block pre code {
    background: none; color: #e2e8f0; padding: 0;
    border: none; font-size: 0.82rem; line-height: 1.6;
}
.code-block .code-html { color: #e2e8f0; }
.code-block .code-html .tag { color: #f472b6; }
.code-block .code-html .attr { color: #93c5fd; }
.code-block .code-html .str { color: #86efac; }
.code-block .code-css .sel { color: #f472b6; }
.code-block .code-css .prop { color: #93c5fd; }
.code-block .code-css .val { color: #86efac; }
.code-block .code-js .kw { color: #c084fc; }
.code-block .code-js .fn { color: #fbbf24; }
.code-block .code-js .str { color: #86efac; }
.code-block .code-js .num { color: #f472b6; }
.theory-box {
    background: rgba(0,0,0,0.25); padding: 1.5rem; border-left: 4px solid var(--accent);
    margin-bottom: 1rem; line-height: 1.7; border-radius: 0 var(--radius) var(--radius) 0;
    backdrop-filter: blur(4px);
}
.theory-box ul, .theory-box ol { padding-left: 1.5rem; }
.theory-box li { margin-bottom: 0.5rem; }
code {
    background: var(--code-bg); color: #6ee7b7; padding: 0.2rem 0.5rem;
    border-radius: 6px; font-family: 'JetBrains Mono', 'Fira Code', monospace; font-size: 0.88em;
    border: 1px solid rgba(110,231,183,0.15);
}
pre {
    background: var(--code-bg); color: #e2e8f0; padding: 1.25rem; border-radius: var(--radius);
    overflow-x: auto; font-family: 'JetBrains Mono', 'Fira Code', monospace;
    border: 1px solid var(--border); font-size: 0.85rem; line-height: 1.5;
}
table {
    width: 100%; border-collapse: separate; border-spacing: 0;
    margin: 1rem 0; font-size: 0.9rem; border-radius: var(--radius);
    background: var(--surface);
}
th, td {
    border-bottom: 1px solid var(--border); padding: 0.75rem; text-align: left;
    background: var(--surface);
}
th {
    background: rgba(var(--accent-rgb),0.08); color: var(--accent); font-weight: 600;
    letter-spacing: 0.02em; text-transform: uppercase; font-size: 0.8rem;
}
td { color: #cbd5e1; }
tr:last-child td { border-bottom: none; }
tr:hover td { background: rgba(255,255,255,0.02); }
td code { font-size: 0.85rem; }
.table-wrap { width: 100%; overflow-x: auto; -webkit-overflow-scrolling: touch; margin: 1rem 0; }
.table-wrap table { margin: 0; }
.interactive-grid { display: grid; grid-template-columns: 1fr 1fr; gap: 1.5rem; margin: 1rem 0; }
button {
    padding: 0.6rem 1.2rem; background: linear-gradient(135deg, var(--accent), var(--teal));
    color: #000; border: none; border-radius: 8px; cursor: pointer; font-weight: 600;
    font-size: 0.85rem; transition: all 0.25s; letter-spacing: 0.01em;
    box-shadow: 0 4px 14px var(--glow);
}
button:hover { transform: translateY(-2px); box-shadow: 0 6px 20px var(--glow); opacity: 1; }
button:active { transform: translateY(0); }
button:focus-visible { outline: 2px solid var(--accent); outline-offset: 2px; }
input, textarea, select {
    padding: 0.65rem; background: var(--bg); border: 1px solid var(--border);
    color: var(--text); border-radius: 8px; font-family: 'JetBrains Mono', monospace;
    font-size: 0.85rem; transition: border-color 0.2s, box-shadow 0.2s;
}
input:focus, textarea:focus, select:focus {
    outline: none; border-color: var(--accent); box-shadow: 0 0 0 3px var(--glow);
}
.img-ref {
    background: var(--bg); border: 1px solid var(--border); border-radius: var(--radius);
    padding: 1rem; margin: 1rem 0; text-align: center;
}
.img-ref img { max-width: 100%; border-radius: 8px; height: auto; }
.attribution { font-size: 0.75rem; color: #64748b; margin-top: 0.5rem; }
.badge {
    font-size: 0.7rem; padding: 0.2rem 0.6rem; border-radius: 999px;
    background: var(--bg); border: 1px solid var(--border); color: #94a3b8;
    font-weight: 500; letter-spacing: 0.02em;
}
.badge.done { background: rgba(16,185,129,0.12); border-color: var(--success); color: var(--success); }
.footer { text-align: center; padding: 2rem 0; color: #475569; font-size: 0.85rem; border-top: 1px solid var(--border); margin-top: 3rem; }
.notification {
    position: fixed; top: 1rem; right: 1rem; padding: 1rem 1.5rem;
    border-radius: var(--radius); z-index: 9999; font-size: 0.9rem;
    transform: translateX(120%); transition: transform 0.4s cubic-bezier(0.22, 1, 0.36, 1);
    max-width: 400px; box-shadow: 0 8px 32px rgba(0,0,0,0.3);
    backdrop-filter: blur(12px);
}
.notification.show { transform: translateX(0); }
.notification.info { background: rgba(var(--accent-rgb),0.9); color: #000; }
.notification.success { background: rgba(16,185,129,0.9); color: white; }
.notification.warning { background: rgba(245,158,11,0.9); color: #000; }
.notification.error { background: rgba(239,68,68,0.9); color: white; }

@media (max-width: 768px) {
    .interactive-grid { grid-template-columns: 1fr; }
    .header h1 { font-size: 1.5rem; }
    .section { padding: 1.25rem; margin: 1rem 0; }
    .lesson-step { padding: 0; }
}
@media (max-width: 640px) { body { padding: 0.5rem; } }