:root {
    --bg-primary: #0d1117;
    --bg-secondary: #161b22;
    --bg-tertiary: #21262d;
    --border-color: #30363d;
    --text-primary: #c9d1d9;
    --text-secondary: #8b949e;
    --text-muted: #6e7681;
    --accent-green: #3fb950;
    --accent-green-dim: #238636;
    --accent-blue: #58a6ff;
    --accent-orange: #d2991d;
    --accent-red: #f85149;
    --accent-purple: #bc8cff;
    --danger-bg: #490202;
    --success-bg: #04260f;
    --warning-bg: #3d2800;
    --info-bg: #041b3d;
    --radius: 8px;
    --radius-sm: 4px;
    --shadow: 0 2px 8px rgba(0,0,0,0.3);
}

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

body {
    font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, Oxygen, sans-serif;
    background: var(--bg-primary);
    color: var(--text-primary);
    line-height: 1.6;
    min-height: 100vh;
    display: flex;
    flex-direction: column;
}

a { color: var(--accent-blue); text-decoration: none; }
a:hover { text-decoration: underline; }

/* Navbar */
.navbar {
    background: var(--bg-secondary);
    border-bottom: 1px solid var(--border-color);
    padding: 0 1.5rem;
    position: sticky;
    top: 0;
    z-index: 100;
}
.nav-container {
    max-width: 1200px;
    margin: 0 auto;
    display: flex;
    align-items: center;
    justify-content: space-between;
    height: 56px;
}
.nav-brand {
    font-size: 1.25rem;
    font-weight: 700;
    color: var(--accent-green) !important;
    text-decoration: none !important;
}
.nav-links { display: flex; align-items: center; gap: 1.25rem; }
.nav-links a { color: var(--text-primary); font-size: 0.9rem; }
.nav-user { color: var(--text-secondary); font-size: 0.85rem; }
.score-badge {
    background: var(--accent-green-dim);
    color: var(--accent-green);
    padding: 0.2rem 0.6rem;
    border-radius: 12px;
    font-size: 0.8rem;
    font-weight: 600;
}

/* Flash messages */
.flash-container { max-width: 1200px; margin: 1rem auto 0; padding: 0 1.5rem; }
.alert { padding: 0.75rem 1rem; border-radius: var(--radius-sm); margin-bottom: 0.5rem; font-size: 0.9rem; }
.alert-success { background: var(--success-bg); color: var(--accent-green); border: 1px solid var(--accent-green-dim); }
.alert-danger { background: var(--danger-bg); color: var(--accent-red); border: 1px solid #660000; }
.alert-info { background: var(--info-bg); color: var(--accent-blue); border: 1px solid #1a4480; }
.alert-warning { background: var(--warning-bg); color: var(--accent-orange); border: 1px solid #665000; }

/* Main content */
.main-content { flex: 1; max-width: 1200px; margin: 2rem auto; padding: 0 1.5rem; width: 100%; }

/* Home page */
.home-header { text-align: center; margin-bottom: 2rem; }
.home-header h1 { font-size: 2.5rem; color: var(--accent-green); }
.subtitle { color: var(--text-secondary); margin-top: 0.5rem; }

.login-bar { text-align: center; margin-bottom: 2rem; }
.login-form { display: flex; gap: 0.5rem; justify-content: center; align-items: center; flex-wrap: wrap; }
.login-form input {
    background: var(--bg-tertiary);
    border: 1px solid var(--border-color);
    color: var(--text-primary);
    padding: 0.5rem 0.75rem;
    border-radius: var(--radius-sm);
    font-size: 0.9rem;
}
.login-form input:focus { outline: none; border-color: var(--accent-green); }
.login-hint { color: var(--text-muted); font-size: 0.8rem; margin-top: 0.5rem; }
.login-hint code { background: var(--bg-tertiary); padding: 0.15rem 0.35rem; border-radius: 3px; font-size: 0.75rem; }

/* Buttons */
.btn {
    padding: 0.5rem 1rem;
    border: none;
    border-radius: var(--radius-sm);
    cursor: pointer;
    font-size: 0.9rem;
    font-weight: 500;
    transition: all 0.15s ease;
}
.btn-primary { background: var(--accent-green-dim); color: var(--accent-green); border: 1px solid var(--accent-green-dim); }
.btn-primary:hover { background: var(--accent-green); color: #000; }
.btn-danger { background: #660000; color: var(--accent-red); border: 1px solid #660000; }
.btn-danger:hover { background: var(--accent-red); color: #000; }
.btn-outline { background: transparent; color: var(--text-secondary); border: 1px solid var(--border-color); }
.btn-outline:hover { border-color: var(--accent-blue); color: var(--accent-blue); }
.btn-sm { padding: 0.3rem 0.65rem; font-size: 0.8rem; }

/* Challenge Cards */
.challenge-grid {
    display: grid;
    grid-template-columns: repeat(auto-fill, minmax(280px, 1fr));
    gap: 1.25rem;
}
.challenge-card {
    background: var(--bg-secondary);
    border: 1px solid var(--border-color);
    border-radius: var(--radius);
    padding: 1.25rem;
    transition: border-color 0.2s, transform 0.2s;
}
.challenge-card:hover {
    border-color: var(--accent-green-dim);
    transform: translateY(-2px);
}
.card-header { display: flex; justify-content: space-between; align-items: center; margin-bottom: 0.5rem; }
.challenge-number {
    font-size: 0.75rem;
    color: var(--text-muted);
    background: var(--bg-tertiary);
    padding: 0.15rem 0.5rem;
    border-radius: 3px;
}
.difficulty-badge {
    font-size: 0.7rem;
    padding: 0.15rem 0.5rem;
    border-radius: 10px;
    text-transform: uppercase;
    font-weight: 600;
    letter-spacing: 0.5px;
}
.badge-easy { background: var(--success-bg); color: var(--accent-green); }
.badge-medium { background: var(--warning-bg); color: var(--accent-orange); }
.badge-hard { background: var(--danger-bg); color: var(--accent-red); }
.challenge-card h3 { font-size: 1.1rem; margin-bottom: 0.5rem; color: var(--text-primary); }
.card-desc { color: var(--text-secondary); font-size: 0.85rem; margin-bottom: 1rem; line-height: 1.4; }
.card-actions { display: flex; align-items: center; gap: 0.5rem; }
.solved-count { font-size: 0.85rem; margin-right: auto; }

/* Scoreboard */
.scoreboard-container { max-width: 600px; margin: 0 auto; }
.scoreboard-container h1 { margin-bottom: 1.5rem; }
.score-table {
    width: 100%;
    border-collapse: collapse;
    background: var(--bg-secondary);
    border: 1px solid var(--border-color);
    border-radius: var(--radius);
    overflow: hidden;
}
.score-table th, .score-table td {
    padding: 0.75rem 1rem;
    text-align: left;
    border-bottom: 1px solid var(--border-color);
}
.score-table th { background: var(--bg-tertiary); color: var(--text-secondary); font-size: 0.85rem; text-transform: uppercase; letter-spacing: 0.5px; }
.score-table tr.highlight { background: rgba(63, 185, 80, 0.08); }
.score-table tr:hover { background: var(--bg-tertiary); }

/* Challenge pages */
.challenge-container { max-width: 900px; margin: 0 auto; }
.challenge-header { margin-bottom: 2rem; }
.challenge-header h1 { color: var(--accent-green); }
.challenge-meta { display: flex; gap: 1rem; margin-top: 0.5rem; color: var(--text-secondary); font-size: 0.9rem; }
.level-nav {
    display: flex;
    gap: 0.5rem;
    margin-bottom: 1.5rem;
    border-bottom: 1px solid var(--border-color);
    padding-bottom: 1rem;
}
.level-nav a {
    padding: 0.5rem 1rem;
    border-radius: var(--radius-sm);
    color: var(--text-secondary);
    font-size: 0.85rem;
    font-weight: 500;
    border: 1px solid transparent;
}
.level-nav a:hover { border-color: var(--border-color); text-decoration: none; }
.level-nav a.active { background: var(--bg-tertiary); color: var(--accent-green); border-color: var(--accent-green-dim); }

.challenge-section {
    background: var(--bg-secondary);
    border: 1px solid var(--border-color);
    border-radius: var(--radius);
    padding: 1.5rem;
    margin-bottom: 1.25rem;
}
.challenge-section h2 { color: var(--accent-blue); margin-bottom: 1rem; font-size: 1.15rem; }

/* Forms in challenges */
.challenge-form { display: flex; flex-direction: column; gap: 0.75rem; max-width: 500px; }
.challenge-form label { color: var(--text-secondary); font-size: 0.85rem; font-weight: 500; }
.challenge-form input,
.challenge-form textarea,
.challenge-form select {
    background: var(--bg-tertiary);
    border: 1px solid var(--border-color);
    color: var(--text-primary);
    padding: 0.6rem 0.75rem;
    border-radius: var(--radius-sm);
    font-family: 'SF Mono', 'Fira Code', monospace;
    font-size: 0.9rem;
}
.challenge-form input:focus,
.challenge-form textarea:focus,
.challenge-form select:focus {
    outline: none;
    border-color: var(--accent-green);
}

.result-box {
    background: var(--bg-primary);
    border: 1px solid var(--border-color);
    border-radius: var(--radius-sm);
    padding: 1rem;
    margin-top: 0.75rem;
    font-family: 'SF Mono', 'Fira Code', monospace;
    font-size: 0.85rem;
    white-space: pre-wrap;
    word-break: break-all;
    max-height: 400px;
    overflow-y: auto;
}

/* Flag submission */
.flag-form {
    display: flex;
    gap: 0.5rem;
    align-items: center;
    margin-top: 1rem;
    flex-wrap: wrap;
}
.flag-form input {
    background: var(--bg-tertiary);
    border: 1px solid var(--border-color);
    color: var(--accent-green);
    padding: 0.5rem 0.75rem;
    border-radius: var(--radius-sm);
    font-family: 'SF Mono', 'Fira Code', monospace;
    font-size: 0.9rem;
    min-width: 250px;
}
.flag-form input:focus { outline: none; border-color: var(--accent-green); }
.flag-feedback { font-size: 0.85rem; margin-left: 0.5rem; }

/* Hint */
.hint-toggle {
    background: var(--bg-tertiary);
    border: 1px solid var(--border-color);
    color: var(--accent-orange);
    padding: 0.3rem 0.75rem;
    border-radius: var(--radius-sm);
    cursor: pointer;
    font-size: 0.8rem;
    margin-top: 0.5rem;
}
.hint-content {
    display: none;
    background: var(--warning-bg);
    border: 1px solid #665000;
    padding: 0.75rem;
    border-radius: var(--radius-sm);
    margin-top: 0.5rem;
    font-size: 0.85rem;
    color: var(--accent-orange);
}

/* Code blocks */
code, pre {
    font-family: 'SF Mono', 'Fira Code', 'Consolas', monospace;
    font-size: 0.85rem;
}
pre {
    background: var(--bg-primary);
    border: 1px solid var(--border-color);
    border-radius: var(--radius-sm);
    padding: 1rem;
    overflow-x: auto;
    margin: 0.75rem 0;
}
code {
    background: var(--bg-tertiary);
    padding: 0.15rem 0.35rem;
    border-radius: 3px;
}

/* Progress bar */
.progress-container { margin: 1rem 0; }
.progress-bar {
    height: 6px;
    background: var(--bg-tertiary);
    border-radius: 3px;
    overflow: hidden;
}
.progress-fill {
    height: 100%;
    background: var(--accent-green);
    transition: width 0.5s ease;
    border-radius: 3px;
}
.progress-label { color: var(--text-secondary); font-size: 0.8rem; margin-top: 0.25rem; }

/* Theory page */
.theory-content article { max-width: 800px; }
.theory-content section { margin-bottom: 2rem; }
.theory-content h2 { color: var(--accent-blue); margin-bottom: 0.75rem; }
.theory-content h1 { color: var(--accent-green); margin-bottom: 2rem; }

/* Footer */
.footer {
    background: var(--bg-secondary);
    border-top: 1px solid var(--border-color);
    padding: 1rem 1.5rem;
    text-align: center;
    color: var(--text-muted);
    font-size: 0.8rem;
}
.footer-banner {
    background: var(--danger-bg);
    color: var(--accent-red);
    padding: 0.5rem;
    margin-bottom: 0.5rem;
    font-weight: 700;
    font-size: 0.85rem;
    border-radius: var(--radius-sm);
}

/* Solved indicator */
.solved-badge {
    display: inline-block;
    background: var(--success-bg);
    color: var(--accent-green);
    padding: 0.2rem 0.6rem;
    border-radius: 10px;
    font-size: 0.8rem;
    font-weight: 600;
}

/* Responsive */
@media (max-width: 768px) {
    .challenge-grid { grid-template-columns: 1fr; }
    .nav-container { flex-direction: column; height: auto; padding: 0.5rem 0; }
    .nav-links { flex-wrap: wrap; justify-content: center; gap: 0.75rem; }
    .home-header h1 { font-size: 1.75rem; }
    .login-form { flex-direction: column; }
}

/* Confetti canvas */
#confetti-canvas {
    position: fixed;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    pointer-events: none;
    z-index: 9999;
}