:root {
    --bg-color: #0f172a;
    --card-bg: #1e293b;
    --text-main: #f8fafc;
    --text-muted: #94a3b8;
    --accent-primary: #3b82f6;
    --accent-secondary: #10b981;
    --border-color: #334155;
    --code-bg: #0b1120;
}

body {
    font-family: 'Segoe UI', system-ui, -apple-system, sans-serif;
    background-color: var(--bg-color);
    background-image: radial-gradient(circle at 20% 0%, rgba(59, 130, 246, 0.12) 0%, transparent 40%), radial-gradient(circle at 80% 100%, rgba(16, 185, 129, 0.08) 0%, transparent 35%);
    color: var(--text-main);
    line-height: 1.6;
    margin: 0;
    padding: 0;
    -ms-overflow-style: none;
    scrollbar-width: none;
}

body::-webkit-scrollbar {
    display: none;
}

header {
    background: linear-gradient(135deg, #1e293b 0%, #0f172a 100%);
    padding: 4rem 2rem;
    text-align: center;
    border-bottom: 2px solid var(--accent-primary);
}

h1 {
    font-size: 2.5rem;
    margin-bottom: 0.5rem;
    color: var(--text-main);
}

h2 {
    color: var(--accent-primary);
    margin-top: 2rem;
    border-bottom: 1px solid var(--border-color);
    padding-bottom: 0.5rem;
}

h3 {
    color: var(--accent-secondary);
}

.subtitle {
    font-size: 1.2rem;
    color: var(--text-muted);
    max-width: 600px;
    margin: 0 auto;
}

.container {
    max-width: 900px;
    margin: 0 auto;
    padding: 2.25rem 2rem 3rem;
}

.card {
    background-color: var(--card-bg);
    border: 1px solid var(--border-color);
    border-radius: 8px;
    padding: 2rem;
    margin-bottom: 2rem;
    box-shadow: 0 8px 20px -8px rgba(2, 6, 23, 0.6);
    transition: transform 0.2s ease;
}

.card:hover {
    transform: translateY(-2px);
    border-color: var(--accent-primary);
}

.intro-card {
    background: linear-gradient(180deg, #273244 0%, #222d3d 100%);
    border-color: #475569;
}

.intro-card:hover {
    border-color: #64748b;
}

.intro-card h2 {
    color: #cbd5e1;
}

details.card {
    padding: 0;
    overflow: hidden;
    scroll-margin-top: 1.25rem;
}

details.card:hover {
    transform: none;
}

.phase-summary {
    display: flex;
    align-items: center;
    justify-content: space-between;
    gap: 1rem;
    padding: 1.5rem 2rem;
    cursor: pointer;
    list-style: none;
}

.phase-summary::-webkit-details-marker {
    display: none;
}

.phase-summary:focus-visible {
    outline: 2px solid var(--accent-primary);
    outline-offset: -2px;
}

.phase-heading {
    display: flex;
    align-items: center;
    gap: 1rem;
    flex-wrap: wrap;
}

.phase-summary h2 {
    margin: 0;
    border-bottom: 0;
    padding-bottom: 0;
}

.phase-summary::after {
    content: '▾';
    color: var(--accent-primary);
    font-size: 1.5rem;
    line-height: 1;
    transition: transform 0.2s ease;
    flex-shrink: 0;
}

details.is-open .phase-summary::after {
    transform: rotate(180deg);
}

.phase-content {
    padding: 0 2rem 2rem;
}

.phase-badge {
    display: inline-block;
    background-color: var(--accent-primary);
    color: white;
    padding: 0.25rem 0.75rem;
    border-radius: 9999px;
    font-size: 0.875rem;
    font-weight: bold;
}

@media (max-width: 640px) {
    .phase-summary {
        padding: 1.25rem 1.25rem 1rem;
        align-items: flex-start;
    }

    .phase-content {
        padding: 0 1.25rem 1.25rem;
    }
}

code {
    font-family: 'Fira Code', Consolas, monospace;
    background-color: var(--code-bg);
    color: #38bdf8;
    padding: 0.2rem 0.4rem;
    border-radius: 4px;
    font-size: 0.9em;
}

pre {
    background-color: var(--code-bg);
    padding: 1rem;
    border-radius: 8px;
    overflow-x: auto;
    border: 1px solid var(--border-color);
}

pre code {
    background-color: transparent;
    padding: 0;
    color: #e2e8f0;
}

.objectives-grid {
    display: grid;
    grid-template-columns: repeat(2, minmax(0, 1fr));
    gap: 1.25rem;
    margin-top: 1.5rem;
}

.objective-card {
    background: linear-gradient(180deg, rgba(15, 23, 42, 0.9) 0%, rgba(15, 23, 42, 0.55) 100%);
    border: 1px solid var(--border-color);
    border-radius: 12px;
    padding: 1.4rem;
}

.objective-card h3 {
    margin-top: 0;
    margin-bottom: 0.75rem;
    color: var(--text-main);
}

.objective-card p {
    margin: 0;
    color: var(--text-muted);
}

.objective-card code {
    font-size: 0.85em;
}

@media (max-width: 760px) {
    .objectives-grid {
        grid-template-columns: 1fr;
    }
}

.bonus-card {
    border-color: #f59e0b;
    background: linear-gradient(180deg, var(--card-bg) 0%, rgba(245, 158, 11, 0.05) 100%);
}

.bonus-card h2 {
    color: #f59e0b;
}

.phase-intro {
    color: var(--text-muted);
    margin-top: 0;
}

.bonus-card .phase-summary::after {
    color: #f59e0b;
}

.bonus-card .phase-summary:focus-visible {
    outline-color: #f59e0b;
}

.bonus-card .phase-badge {
    background-color: #f59e0b;
    color: #0f172a;
}

.bonus-box {
    background-color: rgba(15, 23, 42, 0.75);
    border: 1px solid rgba(245, 158, 11, 0.25);
    border-radius: 10px;
    padding: 1rem 1.25rem;
    margin-top: 1.5rem;
}

.bonus-box h3 {
    margin-top: 0;
}

.optional-hint {
    margin-top: 1.5rem;
    background: rgba(148, 163, 184, 0.12);
    border: 1px solid rgba(148, 163, 184, 0.35);
    border-radius: 10px;
    padding: 0.9rem 1rem;
}

.optional-hint p {
    margin: 0;
    color: #cbd5e1;
}

.uml-card {
    overflow: hidden;
    border-color: #a78bfa;
    background: linear-gradient(180deg, var(--card-bg) 0%, rgba(167, 139, 250, 0.08) 100%);
}

.uml-card .phase-summary::after {
    color: #a78bfa;
}

.uml-card .phase-summary:focus-visible {
    outline-color: #a78bfa;
}

.uml-card .phase-badge {
    background-color: #a78bfa;
    color: #0f172a;
}

.uml-card .phase-summary h2 {
    color: #c4b5fd;
}

.uml-intro {
    color: var(--text-muted);
    margin-bottom: 1.5rem;
}

.mermaid-wrapper {
    background: rgba(11, 17, 32, 0.7);
    border: 1px solid var(--border-color);
    border-radius: 12px;
    padding: 1rem;
    overflow-x: auto;
    -ms-overflow-style: none;
    scrollbar-width: none;
}

.mermaid-wrapper::-webkit-scrollbar {
    display: none;
}

.mermaid {
    min-width: 720px;
}