:root {
    --bg-color: #0a0f1a; /* Dark blue for surf night vibe */
    --text-color: #e0e0e0;
    --accent-color: #00b4d8; /* Teal wave */
    --link-color: #00d4ff;
    --bg-secondary: #1c2333;
    --gradient: linear-gradient(135deg, #0a0f1a, #1c2333);
}

body:not(.dark) {
    --bg-color: #f0f8ff;
    --text-color: #121212;
    --accent-color: #0077b6;
    --link-color: #005f73;
    --bg-secondary: #e0f7fa;
    --gradient: linear-gradient(135deg, #f0f8ff, #e0f7fa);
}

body {
    font-family: 'Roboto', sans-serif;
    background: var(--gradient);
    color: var(--text-color);
    margin: 0;
    padding: 0;
    line-height: 1.6;
    transition: background 0.3s, color 0.3s;
}

header {
    text-align: center;
    padding: 2rem 1rem;
    background: rgba(0, 0, 0, 0.2); /* Subtle overlay */
    position: relative;
}

h1 {
    font-family: 'Orbitron', sans-serif;
    font-size: 2.5rem;
    margin: 0;
    color: var(--accent-color);
    text-shadow: 0 0 10px rgba(0, 180, 216, 0.5); /* Hi-tech glow */
}

.subtitle {
    font-size: 1.2rem;
    margin: 0.5rem 0;
}

#mode-toggle {
    position: absolute;
    top: 1rem;
    right: 1rem;
    background: none;
    border: none;
    font-size: 1.5rem;
    cursor: pointer;
    transition: transform 0.3s;
}

#mode-toggle:hover {
    transform: scale(1.2);
}

main {
    max-width: 1200px;
    margin: 0 auto;
    padding: 1rem;
}

section {
    margin-bottom: 2rem;
}

h2 {
    font-family: 'Orbitron', sans-serif;
    color: var(--accent-color);
    border-bottom: 2px solid var(--accent-color);
    padding-bottom: 0.5rem;
}

ul {
    list-style: none;
    padding: 0;
}

li {
    margin: 0.5rem 0;
    background: var(--bg-secondary);
    padding: 1rem;
    border-radius: 8px;
    box-shadow: 0 4px 8px rgba(0, 0, 0, 0.2);
    transition: transform 0.2s;
}

li:hover {
    transform: translateY(-2px);
}

a {
    color: var(--link-color);
    text-decoration: none;
    font-weight: 500;
}

a:hover {
    text-decoration: underline;
}

#categories {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(300px, 1fr));
    gap: 1rem;
}

.category {
    background: rgba(255, 255, 255, 0.05); /* Subtle surf mist */
    padding: 1rem;
    border-radius: 8px;
}

footer {
    text-align: center;
    padding: 1rem;
    font-size: 0.9rem;
    border-top: 1px solid var(--accent-color);
}

/* Responsive adjustments */
@media (max-width: 768px) {
    h1 { font-size: 2rem; }
    .subtitle { font-size: 1rem; }
    li { padding: 0.75rem; }
    #categories { grid-template-columns: 1fr; }
}