:root {
    --bg: #0b0f15;
    --panel: #111827;
    --panel-alt: #152135;
    --text: #e5e7eb;
    --muted: #9ca3af;
    --accent: #22d3ee;
    --accent-2: #22c55e;
    --border: #1f2937;
    --danger: #f87171;
    --shadow: 0 12px 30px rgba(0, 0, 0, 0.35);
}

* {
    box-sizing: border-box;
}

body {
    margin: 0;
    background: radial-gradient(circle at 20% 20%, rgba(34, 211, 238, 0.05), transparent 25%),
        radial-gradient(circle at 80% 10%, rgba(34, 197, 94, 0.06), transparent 20%),
        var(--bg);
    color: var(--text);
    font-family: system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", sans-serif;
    min-height: 100vh;
}

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

.container {
    max-width: 1100px;
    margin: 0 auto;
    padding: 30px 20px 60px;
}

.topbar {
    display: flex;
    align-items: center;
    justify-content: space-between;
    padding: 16px 20px;
    background: #0f1624;
    border-bottom: 1px solid var(--border);
    position: sticky;
    top: 0;
    z-index: 20;
}

.logo {
    font-weight: 700;
    letter-spacing: 0.5px;
    color: var(--accent);
}

.topbar nav a {
    margin-left: 16px;
    padding: 8px 12px;
    border-radius: 6px;
    color: var(--text);
    transition: background 0.2s ease, color 0.2s ease;
}

.topbar nav a:hover {
    background: var(--panel);
    color: var(--accent);
}

.hero {
    background: linear-gradient(135deg, rgba(34, 211, 238, 0.08), rgba(34, 197, 94, 0.08));
    border: 1px solid var(--border);
    border-radius: 16px;
    padding: 40px;
    box-shadow: var(--shadow);
}

.hero-content h1 {
    margin: 8px 0 12px;
    font-size: 32px;
}

.lead {
    color: var(--muted);
    line-height: 1.6;
}

.intro {
    margin-top: 10px;
    line-height: 1.6;
}

.cta-inline {
    margin-top: 18px;
}

.inline-form {
    margin: 0;
    display: inline-flex;
}

.cta-large {
    padding: 14px 20px;
    font-size: 16px;
}

.plain-list {
    padding-left: 18px;
    margin: 6px 0 10px;
}

.plain-list li {
    color: var(--text);
    margin-bottom: 4px;
}

.eyebrow {
    text-transform: uppercase;
    letter-spacing: 1px;
    color: var(--accent);
    font-size: 12px;
    font-weight: 700;
}

.actions {
    display: flex;
    gap: 12px;
    margin-top: 18px;
    flex-wrap: wrap;
}

.btn {
    display: inline-flex;
    align-items: center;
    justify-content: center;
    gap: 8px;
    padding: 12px 18px;
    border-radius: 10px;
    border: 1px solid transparent;
    font-weight: 700;
    color: var(--text);
    cursor: pointer;
    transition: transform 0.12s ease, box-shadow 0.12s ease, background 0.2s ease, border-color 0.2s ease;
}

.btn.primary {
    background: linear-gradient(120deg, var(--accent), #60a5fa);
    color: #0b0f15;
    box-shadow: 0 8px 20px rgba(34, 211, 238, 0.25);
}

.btn.primary:hover {
    transform: translateY(-1px);
}

.btn.ghost {
    background: transparent;
    border-color: var(--border);
}

.btn.ghost:hover {
    border-color: var(--accent);
    color: var(--accent);
}

.btn.small {
    padding: 8px 12px;
    font-weight: 600;
}

.btn.disabled {
    opacity: 0.6;
    cursor: not-allowed;
}

.card-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(280px, 1fr));
    gap: 24px;
    margin-top: 24px;
}

.card {
    background: var(--panel);
    border: 1px solid var(--border);
    border-radius: 14px;
    box-shadow: var(--shadow);
    display: flex;
    flex-direction: column;
}

.card + .card {
    margin-top: 18px;
}

.card-header, .card-body, .card-footer {
    padding: 18px;
}

.card-header h2 {
    margin: 0;
}

.card-body p {
    margin: 0 0 6px;
    color: var(--muted);
}

.card-footer {
    border-top: 1px solid var(--border);
}

.badge-row {
    margin-top: 8px;
}

.badge {
    display: inline-block;
    padding: 6px 10px;
    border-radius: 8px;
    font-size: 13px;
}

.badge.success {
    background: rgba(34, 197, 94, 0.12);
    color: var(--accent-2);
}

.badge.muted {
    background: rgba(156, 163, 175, 0.1);
    color: var(--muted);
}

.category-tag {
    display: inline-block;
    padding: 6px 10px;
    border-radius: 8px;
    border: 1px solid var(--border);
    background: rgba(17, 24, 39, 0.6);
    color: var(--accent);
    font-size: 12px;
    text-transform: uppercase;
    letter-spacing: 0.5px;
}
.stars {
    font-size: 14px;
    color: #fbbf24;
    margin-left: 10px;
}

.category-block {
    margin-bottom: 20px;
}

.tabs {
    display: flex;
    gap: 10px;
    margin-top: 12px;
}

.tab-btn {
    background: rgba(17, 24, 39, 0.7);
    border: 1px solid var(--border);
    color: var(--text);
    padding: 10px 14px;
    border-radius: 10px;
    cursor: pointer;
    font-weight: 700;
    transition: transform 0.12s ease, border-color 0.2s ease, color 0.2s ease;
}

.tab-btn.active {
    border-color: var(--accent);
    color: var(--accent);
    transform: translateY(-1px);
}

.challenges-list {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(320px, 1fr));
    gap: 16px;
    margin-top: 16px;
}

.challenge-card {
    border: 1px solid var(--border);
    border-radius: 14px;
    background: linear-gradient(145deg, rgba(17, 24, 39, 0.85), rgba(21, 33, 53, 0.9));
    box-shadow: 0 10px 24px rgba(0, 0, 0, 0.35);
}

.challenge-card .card-header {
    border-bottom: 1px solid var(--border);
}

.challenge-card h2 {
    margin-top: 8px;
}

.challenge-card .card-footer {
    display: flex;
    align-items: center;
    justify-content: space-between;
    gap: 10px;
}
.section-header {
    display: flex;
    align-items: center;
    justify-content: space-between;
    gap: 10px;
    margin-top: 10px;
}

.alert {
    padding: 14px 16px;
    border-radius: 10px;
    margin: 16px 0;
    border: 1px solid var(--border);
}

.alert-success {
    background: rgba(34, 197, 94, 0.1);
    color: var(--accent-2);
    border-color: rgba(34, 197, 94, 0.25);
}

.alert-error {
    background: rgba(248, 113, 113, 0.12);
    color: #fecdd3;
    border-color: rgba(248, 113, 113, 0.3);
}

.challenge-statement h2,
.hints h2,
.flag-form label {
    margin-top: 0;
}

.challenge-statement {
    margin-top: 12px;
}

.hint {
    border: 1px dashed var(--border);
    border-radius: 10px;
    padding: 12px;
    margin-bottom: 10px;
    background: var(--panel-alt);
    font-size: 12px;
    line-height: 1.5;
}

.hint.locked {
    background: rgba(156, 163, 175, 0.08);
    border-color: rgba(156, 163, 175, 0.25);
}

.hint.locked .hint-button {
    opacity: 0.65;
    cursor: not-allowed;
}

.hint.locked .hint-content {
    opacity: 0.75;
}

.hint.locked .hint-locked-note {
    color: var(--muted);
}

.hint-header {
    display: flex;
    align-items: center;
    justify-content: space-between;
    color: var(--muted);
    font-weight: 700;
    font-size: 12px;
}

.hint-content {
    margin-top: 8px;
    color: var(--text);
}

.markdown-body p {
    margin: 0 0 10px;
}

.markdown-body code {
    background: rgba(255, 255, 255, 0.06);
    padding: 2px 4px;
    border-radius: 4px;
}

.markdown-body strong {
    color: #e0f2fe;
}
.flag-form {
    display: flex;
    flex-direction: column;
    gap: 12px;
}

.flag-form textarea {
    padding: 10px;
    border-radius: 8px;
    border: 1px solid var(--border);
    background: var(--panel-alt);
    color: var(--text);
}

.flag-form input[type="text"] {
    padding: 12px;
    border-radius: 8px;
    border: 1px solid var(--border);
    background: var(--panel-alt);
    color: var(--text);
}

.flag-form input[type="text"]:focus {
    outline: 2px solid var(--accent);
}

.footer {
    border-top: 1px solid var(--border);
    padding: 18px 20px 40px;
    text-align: center;
    color: var(--muted);
    background: #0f1624;
}

@media (max-width: 700px) {
    .section-header {
        flex-direction: column;
        align-items: flex-start;
    }
    .topbar {
        flex-direction: column;
        align-items: flex-start;
        gap: 8px;
    }
    .hero {
        padding: 26px;
    }
}