:root {
    --bg: #f6f8fb;
    --card: #fff;
    --muted: #6b7280;
    --accent: #2563eb;
    --shadow: 0 4px 12px rgba(16, 24, 40, 0.06);
    --radius: 8px;
    --mono: 'JetBrains Mono', monospace;
}
* { box-sizing: border-box; margin: 0; padding: 0; }
html, body {
    height: 100%;
}
body {
    font-family: Inter, sans-serif;
    background: var(--bg);
    color: #0f172a;
    padding: 16px;
    display: flex;
    justify-content: center;
    align-items: center;
}
.wrap {
    width: 100%;
    max-width: 1100px;
}
header {
    margin-bottom: 14px;
}
header h1 {
    font-size: 1.6rem;
    color: #111827;
}
header p {
    color: var(--muted);
    font-size: 0.9rem;
}
.content {
    display: grid;
    grid-template-columns: 1fr 1fr;
    gap: 12px;
}
.content.single-column {
    grid-template-columns: 1fr;
}
.card {
    background: var(--card);
    border-radius: var(--radius);
    box-shadow: var(--shadow);
    padding: 12px;
}
/* Search/filter controls */
.search-controls {
    margin-bottom: 12px;
    display: flex;
    gap: 8px;
}
.search-input {
    flex: 1;
    padding: 6px 10px;
    border: 1px solid #e5e7eb;
    border-radius: 4px;
    font-size: 0.9rem;
}
.filter-select {
    padding: 6px 8px;
    border: 1px solid #e5e7eb;
    border-radius: 4px;
    font-size: 0.9rem;
    background: white;
}
/* Problems list */
.problems-list .problem-item {
    padding: 8px;
    border-bottom: 1px solid #e5e7eb;
    display: flex;
    justify-content: space-between;
    align-items: center;
}
.problem-item:last-child {
    border-bottom: none;
}
.problem-item a {
    text-decoration: none;
    color: #0077ff;
    font-weight: 600;
}
/* Difficulty badge */
.difficulty {
    display: inline-flex;
    align-items: center;
    padding: 0.25em 0.6em;
    border-radius: 10px;
    font-size: 0.85em;
    font-weight: bold;
    text-transform: uppercase;
    color: white;
    white-space: nowrap;
}
.difficulty[data-difficulty="easy"] {
    background-color: #4CAF50; /* Green */
}
.difficulty[data-difficulty="medium"] {
    background-color: #FFC107; /* Amber */
    color: #333;
}
.difficulty[data-difficulty="hard"] {
    background-color: #F44336; /* Red */
}
/* Leaderboard */
.leaderboard-head {
    display: flex;
    justify-content: space-between;
    align-items: center;
    margin-bottom: 6px;
}
.leaderboard-controls {
    display: flex;
    gap: 8px;
    margin-bottom: 12px;
}
.leaderboard-table {
    width: 100%;
    border-collapse: collapse;
    font-size: 0.9rem;
}
.leaderboard-table th,
.leaderboard-table td {
    padding: 6px 8px;
    border-bottom: 1px solid #e5e7eb;
    text-align: left;
}
.leaderboard-table th {
    background: #f9fafb;
    font-weight: 600;
    color: var(--muted);
}
.leaderboard-table tr:hover {
    background: #f3f4f6;
}
/* Sort indicators */
.sortable {
    cursor: pointer;
    position: relative;
    padding-right: 16px;
}
.sortable::after {
    content: "↕";
    position: absolute;
    right: 4px;
    top: 50%;
    transform: translateY(-50%);
    font-size: 0.8em;
    opacity: 0.5;
}
.sort-asc::after {
    content: "↑";
    opacity: 1;
}
.sort-desc::after {
    content: "↓";
    opacity: 1;
}
/* Toggle button */
.btn {
    border: none;
    background: transparent;
    cursor: pointer;
    color: var(--accent);
    font-size: 0.85rem;
    padding: 4px 6px;
    border-radius: 4px;
}
.btn:hover {
    background: rgba(37, 99, 235, 0.08);
}
.btn.active {
    background: rgba(37, 99, 235, 0.15);
}
@media (max-width: 800px) {
    .content { grid-template-columns: 1fr; }
    .leaderboard-controls {
        flex-direction: column;
    }
}