:root {
    --oj-primary: #3b82f6;
    --oj-primary-dark: #2563eb;
    --oj-accent: #f59e0b;
    --oj-accent-soft: #fef3c7;
    --oj-bg: #f0f4f8;
    --oj-surface: #ffffff;
    --oj-text: #1e293b;
    --oj-text-muted: #64748b;
    --oj-nav-bg: rgba(15, 23, 42, 0.92);
    --oj-shadow: 0 4px 24px rgba(15, 23, 42, 0.08);
    --oj-shadow-hover: 0 12px 40px rgba(15, 23, 42, 0.14);
    --oj-radius: 14px;
    --oj-transition: 0.35s cubic-bezier(0.4, 0, 0.2, 1);
    --oj-surface-glass: rgba(255, 255, 255, 0.78);
    --oj-border: rgba(148, 163, 184, 0.22);
    --oj-focus: 0 0 0 4px rgba(59, 130, 246, 0.18);
}

@media (prefers-reduced-motion: reduce) {
    *, *::before, *::after {
        animation-duration: 0.01ms !important;
        animation-iteration-count: 1 !important;
        transition-duration: 0.01ms !important;
    }
}

body {
    background-color: var(--oj-bg);
    color: var(--oj-text);
    font-family: system-ui, -apple-system, "Segoe UI", Roboto, "PingFang SC", "Microsoft YaHei", sans-serif;
    min-height: 100vh;
    display: flex;
    flex-direction: column;
    letter-spacing: -0.005em;
}

body::before {
    content: "";
    position: fixed;
    inset: 0;
    background:
        radial-gradient(ellipse 80% 50% at 20% -10%, rgba(59, 130, 246, 0.12), transparent),
        radial-gradient(ellipse 60% 40% at 90% 10%, rgba(245, 158, 11, 0.1), transparent);
    pointer-events: none;
    z-index: -1;
}

main.container {
    flex: 1;
}

/* Navbar */
.oj-navbar {
    background: var(--oj-nav-bg) !important;
    backdrop-filter: blur(20px) saturate(150%);
    box-shadow: 0 1px 0 rgba(255, 255, 255, 0.06);
    transition: box-shadow var(--oj-transition);
}

.oj-navbar.scrolled {
    box-shadow: 0 4px 24px rgba(0, 0, 0, 0.2);
}

.navbar-brand {
    font-weight: 700;
    font-size: 1.2rem;
    background: linear-gradient(135deg, #93c5fd, #fbbf24);
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    background-clip: text;
    letter-spacing: -0.025em;
    transition: opacity 180ms ease, transform 220ms ease;
}

.navbar-brand:hover {
    opacity: 0.84;
    transform: translateY(-1px);
}

.nav-link {
    position: relative;
    transition: color var(--oj-transition);
}

.nav-link::after {
    content: "";
    position: absolute;
    left: 0.75rem;
    right: 0.75rem;
    bottom: 0.35rem;
    height: 2px;
    background: linear-gradient(90deg, var(--oj-primary), var(--oj-accent));
    transform: scaleX(0);
    transition: transform var(--oj-transition);
    border-radius: 1px;
}

.nav-link:hover::after,
.nav-link.active::after {
    transform: scaleX(1);
}

/* Cards (global) */
.card {
    border: none;
    border-radius: var(--oj-radius);
    box-shadow: var(--oj-shadow);
    margin-bottom: 1.25rem;
    border: 1px solid var(--oj-border);
    transition: transform 260ms cubic-bezier(0.2, 0.8, 0.2, 1), box-shadow 260ms ease, border-color 260ms ease;
    overflow: hidden;
}

.card:hover {
    box-shadow: var(--oj-shadow-hover);
    border-color: rgba(59, 130, 246, 0.18);
}

.btn, .form-control, .form-select {
    transition: transform 180ms ease, box-shadow 180ms ease, border-color 180ms ease, background-color 180ms ease;
}

.btn:focus-visible, .form-control:focus, .form-select:focus {
    box-shadow: var(--oj-focus);
}

.btn:active {
    transform: scale(0.98);
}

/* Difficulty & status — use slugified class names
   (see ``Problem.difficulty_slug``) so the selectors are unambiguous
   regardless of ``+`` / ``-`` suffixes. */
.difficulty-badge { font-size: 0.8rem; }
.difficulty-intro      { background-color: #2ecc71; }
.difficulty-pminus     { background-color: #3498db; }
.difficulty-puhui      { background-color: #9b59b6; }
.difficulty-pplus      { background-color: #e67e22; }
.difficulty-tminus     { background-color: #e74c3c; }
.difficulty-tigao      { background-color: #c0392b; }
.difficulty-tplus      { background-color: #8e44ad; }
.difficulty-shengxuan  { background-color: #1abc9c; }
.difficulty-noi        { background-color: #f39c12; }
.status-Accepted { color: #2ecc71; font-weight: bold; }
.status-Wrong { color: #e74c3c; font-weight: bold; }
.status-Pending { color: #f39c12; font-weight: bold; }
.status-Error { color: #c0392b; font-weight: bold; }
.code-editor {
    font-family: 'Courier New', Consolas, monospace;
    min-height: 300px;
}

/* Footer */
.oj-footer {
    background: linear-gradient(180deg, #0f172a, #1e293b);
    border-top: 1px solid rgba(255, 255, 255, 0.06);
}

/* Home page */
.home-hero {
    position: relative;
    border-radius: calc(var(--oj-radius) + 4px);
    padding: clamp(2.25rem, 6vw, 4.5rem) clamp(1.5rem, 5vw, 3.5rem);
    margin-bottom: 2rem;
    overflow: hidden;
    background: linear-gradient(135deg, rgba(30, 58, 95, 0.98), rgba(15, 23, 42, 0.98) 58%, rgba(30, 41, 59, 0.96));
    box-shadow: 0 24px 70px rgba(15, 23, 42, 0.2);
    color: #fff;
}

.home-hero::before,
.home-hero::after {
    content: "";
    position: absolute;
    border-radius: 50%;
    filter: blur(60px);
    opacity: 0.5;
    animation: hero-float 10s ease-in-out infinite;
}

.home-hero::before {
    width: min(70vw, 280px);
    height: min(70vw, 280px);
    background: #3b82f6;
    top: -80px;
    right: -40px;
}

.home-hero::after {
    width: min(50vw, 200px);
    height: min(50vw, 200px);
    background: #f59e0b;
    bottom: -60px;
    left: 10%;
    animation-delay: -4s;
}

@keyframes hero-float {
    0%, 100% { transform: translate(0, 0) scale(1); }
    50% { transform: translate(20px, -15px) scale(1.05); }
}

.hero-content {
    position: relative;
    z-index: 1;
}

.hero-title {
    font-size: clamp(1.75rem, 4vw, 2.5rem);
    font-weight: 800;
    letter-spacing: -0.045em;
    margin-bottom: 0.75rem;
}

.hero-title span {
    background: linear-gradient(90deg, #93c5fd, #fcd34d);
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    background-clip: text;
}

.hero-subtitle {
    font-size: 1.1rem;
    color: rgba(255, 255, 255, 0.75);
    max-width: 32rem;
    margin-bottom: 1.75rem;
    line-height: 1.6;
}

.hero-actions {
    display: flex;
    flex-wrap: wrap;
    gap: 0.75rem;
}

.hero-actions .btn {
    padding: 0.65rem 1.25rem;
    font-weight: 600;
    border-radius: 10px;
    transition: transform 220ms cubic-bezier(0.2, 0.8, 0.2, 1), box-shadow 220ms ease, filter 220ms ease;
}

.hero-actions .btn:hover {
    transform: translateY(-2px);
    box-shadow: 0 8px 24px rgba(0, 0, 0, 0.25);
    filter: brightness(1.06);
}

.btn-hero-primary {
    background: linear-gradient(135deg, var(--oj-primary), var(--oj-primary-dark));
    border: none;
    color: #fff;
}

.btn-hero-accent {
    background: linear-gradient(135deg, #f59e0b, #d97706);
    border: none;
    color: #fff;
}

/* Stats row */
.stats-row {
    display: grid;
    grid-template-columns: repeat(3, 1fr);
    gap: 1rem;
    margin-bottom: 2rem;
}

@media (max-width: 576px) {
    .stats-row { grid-template-columns: 1fr; }
}

.stat-card {
    background: var(--oj-surface-glass);
    backdrop-filter: blur(18px) saturate(130%);
    border: 1px solid var(--oj-border);
    border-radius: var(--oj-radius);
    padding: 1.25rem 1.5rem;
    text-align: center;
    box-shadow: var(--oj-shadow);
    transition: transform var(--oj-transition), box-shadow var(--oj-transition);
}

.stat-card:hover {
    transform: translateY(-3px);
    box-shadow: var(--oj-shadow-hover);
}

.stat-value {
    font-size: 2rem;
    font-weight: 800;
    color: var(--oj-primary);
    line-height: 1.2;
}

.stat-label {
    font-size: 0.875rem;
    color: var(--oj-text-muted);
    margin-top: 0.25rem;
}

/* Feature cards */
.feature-grid {
    display: grid;
    grid-template-columns: repeat(3, 1fr);
    gap: 1.25rem;
    margin-bottom: 2rem;
}

@media (max-width: 768px) {
    .feature-grid { grid-template-columns: 1fr; }
}

.feature-card {
    background: var(--oj-surface-glass);
    backdrop-filter: blur(18px) saturate(130%);
    border-radius: var(--oj-radius);
    padding: 1.75rem 1.5rem;
    text-align: center;
    box-shadow: var(--oj-shadow);
    transition: transform var(--oj-transition), box-shadow var(--oj-transition);
    border: 1px solid rgba(59, 130, 246, 0.08);
}

.feature-card:hover {
    transform: translateY(-3px);
    box-shadow: var(--oj-shadow-hover);
    border-color: rgba(59, 130, 246, 0.2);
}

.feature-icon {
    width: 64px;
    height: 64px;
    margin: 0 auto 1rem;
    border-radius: 16px;
    display: flex;
    align-items: center;
    justify-content: center;
    font-size: 1.75rem;
    transition: transform var(--oj-transition);
}

.feature-card:hover .feature-icon {
    transform: scale(1.04);
}

.feature-icon.blue { background: linear-gradient(135deg, #dbeafe, #93c5fd); color: #2563eb; }
.feature-icon.amber { background: linear-gradient(135deg, #fef3c7, #fcd34d); color: #d97706; }
.feature-icon.rose { background: linear-gradient(135deg, #ffe4e6, #fda4af); color: #e11d48; }

/* Animations */
.animate-in {
    opacity: 0;
    transform: translateY(24px);
}

.animate-in.visible {
    opacity: 1;
    transform: translateY(0);
    transition: opacity 0.6s cubic-bezier(0.4, 0, 0.2, 1),
                transform 0.6s cubic-bezier(0.4, 0, 0.2, 1);
}

.animate-in.delay-1 { transition-delay: 0.1s; }
.animate-in.delay-2 { transition-delay: 0.2s; }
.animate-in.delay-3 { transition-delay: 0.3s; }
.animate-in.delay-4 { transition-delay: 0.4s; }
.animate-in.delay-5 { transition-delay: 0.5s; }

/* Recent problems table */
.recent-table tbody tr {
    transition: background-color 0.2s ease, transform 0.2s ease;
}

.recent-table tbody tr:hover {
    background-color: rgba(59, 130, 246, 0.06);
}

.home-hero .btn-outline-light {
    border-color: rgba(255, 255, 255, 0.38);
    background: rgba(255, 255, 255, 0.08);
    backdrop-filter: blur(12px);
}

.home-hero .btn-outline-light:hover {
    background: rgba(255, 255, 255, 0.16);
}

.recent-table a {
    text-decoration: none;
    font-weight: 500;
    color: var(--oj-primary-dark);
    transition: color 0.2s ease;
}

.recent-table a:hover {
    color: var(--oj-primary);
}

/* Sidebar quick links */
.quick-link-item {
    border: none !important;
    padding: 0.85rem 0 !important;
    transition: padding-left 0.25s ease, background-color 0.25s ease;
    border-radius: 8px;
}

.quick-link-item:hover {
    padding-left: 0.5rem !important;
    background-color: rgba(59, 130, 246, 0.06);
}

@media (prefers-reduced-transparency: reduce) {
    .oj-navbar, .stat-card, .feature-card, .home-hero .btn-outline-light {
        backdrop-filter: none;
    }

    .stat-card, .feature-card {
        background: var(--oj-surface);
    }
}

.quick-link-item a {
    text-decoration: none;
    color: var(--oj-text);
    display: flex;
    align-items: center;
    gap: 0.5rem;
}

.quick-link-item a i {
    color: var(--oj-primary);
    transition: transform 0.25s ease;
}

.quick-link-item:hover a i {
    transform: translateX(4px);
}

/* Reading and submission surfaces */
.problem-detail-layout,
.submission-layout {
    align-items: flex-start;
}

.problem-titlebar,
.submission-titlebar {
    background: linear-gradient(135deg, #172033, #263a5b);
    color: #fff;
    border: 0;
    padding: 1rem 1.25rem;
}

.problem-titlebar h5,
.submission-titlebar h5 {
    letter-spacing: -0.02em;
}

.problem-section-title {
    display: flex;
    align-items: center;
    gap: 0.6rem;
    margin-bottom: 0.85rem;
    color: #0f172a;
    font-size: 0.95rem;
    letter-spacing: -0.01em;
}

.problem-section-title::before {
    content: "";
    width: 0.3rem;
    height: 1.15rem;
    border-radius: 999px;
    background: var(--oj-primary);
}

.problem-sidebar-stack,
.submission-sidebar-stack {
    position: sticky;
    top: 5.5rem;
}

.problem-sidebar-card,
.submission-sidebar-card,
.problem-actions-card {
    background: var(--oj-surface-glass);
    backdrop-filter: blur(18px) saturate(130%);
}

.problem-sidebar-card + .problem-sidebar-card,
.problem-sidebar-card + .problem-actions-card,
.submission-sidebar-card + .submission-sidebar-card {
    margin-top: 1rem;
}

.problem-actions-card {
    margin-top: 1rem;
}



.submission-actions {
    display: flex;
    gap: 0.65rem;
    align-items: center;
    padding-top: 0.4rem;
}

.submission-actions .btn-primary {
    min-width: 7.5rem;
    box-shadow: 0 8px 18px rgba(37, 99, 235, 0.2);
}

.submission-language-field .form-select {
    max-width: 22rem;
    border-radius: 10px;
}

@media (max-width: 991.98px) {
    .problem-sidebar-stack,
    .submission-sidebar-stack {
        position: static;
    }
}

@media (prefers-reduced-transparency: reduce) {
    .problem-sidebar-card,
    .submission-sidebar-card,
    .problem-actions-card {
        backdrop-filter: none;
        background: var(--oj-surface);
    }
}

.section-header {
    display: flex;
    align-items: center;
    gap: 0.5rem;
    font-weight: 600;
}

.card-header-gradient {
    background: linear-gradient(135deg, #f8fafc, #f1f5f9);
    border-bottom: 1px solid #e2e8f0;
}

/* Steps list */
.steps-list {
    counter-reset: step;
    list-style: none;
    padding: 0;
    margin: 0;
}

.steps-list li {
    position: relative;
    padding-left: 2.5rem;
    margin-bottom: 1rem;
    color: var(--oj-text-muted);
    line-height: 1.5;
}

.steps-list li::before {
    counter-increment: step;
    content: counter(step);
    position: absolute;
    left: 0;
    top: 0;
    width: 1.75rem;
    height: 1.75rem;
    background: linear-gradient(135deg, var(--oj-primary), var(--oj-primary-dark));
    color: #fff;
    border-radius: 50%;
    font-size: 0.8rem;
    font-weight: 700;
    display: flex;
    align-items: center;
    justify-content: center;
}