:root {
    --bg-color: #0f172a;
    --text-color: #e2e8f0;
    --accent-color: #38bdf8;
    --success-color: #10b981;
    --danger-color: #ef4444;
    --surface-color: #1e293b;
    --border-color: #334155;
    --hover-color: #0ea5e9;
    --code-bg: #0b1120;
}

* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
}

body {
    font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
    background-color: var(--bg-color);
    color: var(--text-color);
    line-height: 1.6;
}

.container {
    max-width: 1200px;
    margin: 0 auto;
    padding: 0 20px;
}

header {
    background-color: var(--surface-color);
    border-bottom: 1px solid var(--border-color);
    padding: 1.5rem 0;
    position: sticky;
    top: 0;
    z-index: 100;
}

.header-content {
    display: flex;
    align-items: center;
    gap: 20px;
}

.brand .logo {
    width: 200px;
    height: auto;
}

.header-content h1 {
    color: var(--accent-color);
    font-size: 2rem;
    margin-bottom: 0.2rem;
}

.header-content p {
    font-size: 0.9rem;
    color: #94a3b8;
}

main {
    display: flex;
    gap: 3rem;
    padding: 3rem 20px;
}

.sidebar {
    width: 250px;
    flex-shrink: 0;
}

.sidebar nav {
    position: sticky;
    top: 120px;
}

.sidebar ul {
    list-style: none;
}

.sidebar a {
    color: var(--text-color);
    text-decoration: none;
    display: block;
    padding: 12px 15px;
    border-radius: 8px;
    transition: all 0.3s ease;
    border: 1px solid transparent;
    margin-bottom: 5px;
    font-weight: 500;
}

.sidebar a:hover {
    background-color: rgba(56, 189, 248, 0.1);
    color: var(--accent-color);
}

.sidebar a.active {
    background-color: rgba(56, 189, 248, 0.2);
    border-color: var(--accent-color);
    color: var(--accent-color);
    box-shadow: inset 4px 0 0 var(--accent-color);
}

.sidebar a.quiz-link {
    background-color: rgba(16, 185, 129, 0.1);
    color: var(--success-color);
    border: 1px solid var(--success-color);
    margin-top: 15px;
}

.sidebar a.quiz-link:hover, .sidebar a.quiz-link.active {
    background-color: var(--success-color);
    color: #fff;
}

.content {
    flex-grow: 1;
    max-width: 800px;
}

.level-section {
    display: none;
    background-color: var(--surface-color);
    padding: 2.5rem;
    border-radius: 12px;
    border: 1px solid var(--border-color);
    box-shadow: 0 4px 6px -1px rgba(0, 0, 0, 0.1);
    animation: fadeIn 0.4s ease-out;
}

.level-section.active {
    display: block;
}

@keyframes fadeIn {
    from { opacity: 0; transform: translateY(10px); }
    to { opacity: 1; transform: translateY(0); }
}

.level-section h2 {
    color: var(--accent-color);
    margin-bottom: 1.5rem;
    padding-bottom: 0.5rem;
    border-bottom: 1px solid var(--border-color);
}

.concept-box {
    background-color: rgba(56, 189, 248, 0.05);
    border-left: 4px solid var(--accent-color);
    padding: 15px 20px;
    margin-bottom: 1.5rem;
    border-radius: 0 8px 8px 0;
    font-style: italic;
    color: #bae6fd;
}

article p { margin-bottom: 1.5rem; }
article ul { margin-bottom: 1.5rem; padding-left: 1.5rem; }
article li { margin-bottom: 0.5rem; }
article h3 { color: #f8fafc; margin: 2rem 0 1rem 0; font-size: 1.3rem; }

code {
    background-color: var(--code-bg);
    padding: 0.2rem 0.4rem;
    border-radius: 4px;
    font-family: monospace;
    font-size: 0.9em;
    color: #fca5a5;
}

.code-block {
    position: relative;
    background-color: var(--code-bg);
    border-radius: 8px;
    margin: 1.5rem 0;
    border: 1px solid var(--border-color);
    overflow: hidden;
}

.code-block pre { padding: 1.5rem; overflow-x: auto; }
.code-block pre code { background: none; padding: 0; color: #e2e8f0; }

.copy-btn {
    position: absolute;
    top: 10px; right: 10px;
    background-color: var(--surface-color);
    color: var(--text-color);
    border: 1px solid var(--border-color);
    padding: 5px 12px; border-radius: 6px;
    cursor: pointer; font-size: 0.8rem;
    transition: all 0.2s ease;
}
.copy-btn:hover { background-color: var(--accent-color); color: #fff; }

/* QUIZ STYLES */
.quiz-container {
    text-align: center;
}
.action-btn {
    background-color: var(--accent-color);
    color: #fff; border: none;
    padding: 12px 24px; border-radius: 8px;
    font-size: 1.1rem; cursor: pointer; font-weight: bold;
    transition: background 0.3s; margin-top: 15px;
}
.action-btn:hover { background-color: var(--hover-color); }

.quiz-header {
    display: flex; flex-direction: column; gap: 10px;
    margin-bottom: 20px; align-items: center;
}
.timer-bar {
    width: 100%; max-width: 400px; height: 10px;
    background-color: var(--border-color); border-radius: 5px; overflow: hidden;
}
#timer-fill {
    height: 100%; width: 100%; background-color: var(--success-color);
    transition: width 1s linear, background-color 0.3s;
}
.question-text {
    font-size: 1.3rem; margin-bottom: 30px; font-weight: 500;
}
.options-grid {
    display: grid; grid-template-columns: 1fr; gap: 15px; max-width: 500px; margin: 0 auto;
}
.option-btn {
    background-color: var(--bg-color); color: var(--text-color);
    border: 1px solid var(--border-color); padding: 15px; border-radius: 8px;
    font-size: 1rem; cursor: pointer; transition: all 0.2s; text-align: left;
}
.option-btn:hover { border-color: var(--accent-color); background-color: rgba(56, 189, 248, 0.1); }
.option-btn.correct { background-color: var(--success-color); color: white; border-color: var(--success-color); }
.option-btn.wrong { background-color: var(--danger-color); color: white; border-color: var(--danger-color); }
.score { font-size: 2rem; font-weight: bold; color: var(--accent-color); margin: 20px 0; }

@media (max-width: 768px) {
    main { flex-direction: column; }
    .sidebar { width: 100%; }
    .sidebar nav { position: static; }
}