:root {
    --bg:        #0a0e1a;
    --bg-card:   #0f1525;
    --bg-term:   #060b14;
    --blue:      #00b4ff;
    --blue-dim:  #0077aa;
    --neon:      #00e5ff;
    --neon-pink: #ff2d7b;
    --white:     #e0e8f0;
    --grey:      #5a6a80;
    --border:    #1a2540;
    --font-mono: 'Courier New', 'Lucida Console', monospace;
    --font-sans: 'Segoe UI', 'Helvetica Neue', Arial, sans-serif;
}

/* ── Light mode overrides ──────────────────────────── */
html.light {
    --bg:        #f0f2f5;
    --bg-card:   #ffffff;
    --bg-term:   #f7f8fa;
    --blue:      #0070cc;
    --blue-dim:  #0058a3;
    --neon:      #0070cc;
    --neon-pink: #d6336c;
    --white:     #1a1a2e;
    --grey:      #5a6070;
    --border:    #d0d5dd;
}

html.light header h1 {
    text-shadow: none;
}

html.light .sudoku-grid input.original {
    text-shadow: none;
}

html.light .sudoku-grid input.solved {
    text-shadow: none;
}

html.light .status-bar.ready {
    box-shadow: none;
}

html.light .status-bar.error {
    box-shadow: none;
}

html.light #solve-btn:hover:not(:disabled) {
    box-shadow: none;
}

html.light #random-btn:hover {
    box-shadow: none;
}

* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
}

body {
    font-family: var(--font-sans);
    background: var(--bg);
    min-height: 100vh;
    color: var(--white);
    transition: background 0.3s ease, color 0.3s ease;
}

.container {
    max-width: 1200px;
    margin: 0 auto;
    padding: 20px;
}

/* Header row with theme toggle */
.header-row {
    display: flex;
    justify-content: center;
    align-items: center;
    gap: 20px;
    position: relative;
}

.theme-toggle {
    position: absolute;
    right: 0;
    background: var(--bg-term);
    border: 1px solid var(--border);
    border-radius: 6px;
    padding: 8px 12px;
    cursor: pointer;
    font-size: 1.2rem;
    transition: all 0.2s ease;
}

.theme-toggle:hover {
    border-color: var(--neon);
}

/* Show/hide icons based on theme */
.icon-light {
    display: none;
}

html.light .icon-dark {
    display: none;
}

html.light .icon-light {
    display: inline;
}

header {
    text-align: center;
    margin-bottom: 20px;
    padding: 20px 0;
    border-bottom: 1px solid var(--border);
}

header h1 {
    font-family: var(--font-mono);
    font-size: 2.5rem;
    color: var(--neon);
    text-shadow: 0 0 20px rgba(0, 229, 255, 0.5), 0 0 40px rgba(0, 229, 255, 0.3);
    letter-spacing: 2px;
}

.subtitle {
    font-family: var(--font-mono);
    color: var(--grey);
    margin-top: 8px;
    font-size: 0.9rem;
}

.status-bar {
    background: var(--bg-term);
    padding: 12px 20px;
    border-radius: 4px;
    margin-bottom: 20px;
    display: flex;
    align-items: center;
    justify-content: center;
    gap: 10px;
    border: 1px solid var(--border);
    font-family: var(--font-mono);
    font-size: 0.85rem;
}

.status-bar.ready {
    border-color: var(--neon);
    box-shadow: 0 0 10px rgba(0, 229, 255, 0.2);
}

.status-bar.ready #status-text {
    color: var(--neon);
}

.status-bar.error {
    border-color: var(--neon-pink);
    box-shadow: 0 0 10px rgba(255, 45, 123, 0.2);
}

.status-bar.error #status-text {
    color: var(--neon-pink);
}

.loader {
    width: 16px;
    height: 16px;
    border: 2px solid var(--border);
    border-top-color: var(--neon);
    border-radius: 50%;
    animation: spin 1s linear infinite;
}

.loader.hidden {
    display: none;
}

@keyframes spin {
    to { transform: rotate(360deg); }
}

main {
    display: flex;
    flex-direction: column;
    gap: 30px;
}

.solver-section {
    display: grid;
    grid-template-columns: 1fr 1fr;
    gap: 30px;
}

@media (max-width: 900px) {
    .solver-section {
        grid-template-columns: 1fr;
    }
}

.grid-container, .results-container, .log-section {
    background: var(--bg-card);
    padding: 24px;
    border-radius: 6px;
    border: 1px solid var(--border);
}

h2 {
    font-family: var(--font-mono);
    color: var(--blue);
    margin-bottom: 16px;
    font-size: 1.1rem;
    text-transform: uppercase;
    letter-spacing: 1px;
}

h2::before {
    content: '> ';
    color: var(--neon-pink);
}

.sudoku-grid {
    display: grid;
    grid-template-columns: repeat(9, 1fr);
    gap: 1px;
    background: var(--border);
    padding: 1px;
    border-radius: 4px;
    margin-bottom: 16px;
}

.sudoku-grid input {
    width: 100%;
    aspect-ratio: 1;
    text-align: center;
    font-family: var(--font-mono);
    font-size: 1.2rem;
    font-weight: bold;
    border: none;
    background: var(--bg-term);
    color: var(--white);
    outline: none;
    transition: all 0.15s ease;
}

.sudoku-grid input:focus {
    background: var(--bg-card);
    box-shadow: inset 0 0 10px rgba(0, 180, 255, 0.3);
}

.sudoku-grid input.original {
    color: var(--neon);
    text-shadow: 0 0 8px rgba(0, 229, 255, 0.5);
}

.sudoku-grid input.solved {
    color: var(--neon-pink);
    text-shadow: 0 0 8px rgba(255, 45, 123, 0.5);
}

.sudoku-grid input.invalid {
    background: rgba(255, 45, 123, 0.1);
    color: var(--neon-pink);
}

/* Block borders - 3x3 grid separators */
.sudoku-grid input:nth-child(3n):not(:nth-child(9n)) {
    border-right: 2px solid var(--blue-dim);
}

.sudoku-grid input:nth-child(n+19):nth-child(-n+27),
.sudoku-grid input:nth-child(n+46):nth-child(-n+54) {
    border-bottom: 2px solid var(--blue-dim);
}

.button-group {
    display: flex;
    gap: 10px;
    margin-bottom: 16px;
    flex-wrap: wrap;
}

button {
    padding: 10px 20px;
    font-family: var(--font-mono);
    font-size: 0.85rem;
    border: 1px solid var(--border);
    border-radius: 4px;
    cursor: pointer;
    transition: all 0.2s ease;
    text-transform: uppercase;
    letter-spacing: 1px;
}

button:disabled {
    opacity: 0.4;
    cursor: not-allowed;
}

#solve-btn {
    background: transparent;
    color: var(--neon);
    border-color: var(--neon);
}

#solve-btn:hover:not(:disabled) {
    background: var(--neon);
    color: var(--bg);
    box-shadow: 0 0 20px rgba(0, 229, 255, 0.4);
}

#clear-btn {
    background: transparent;
    color: var(--grey);
    border-color: var(--grey);
}

#clear-btn:hover {
    color: var(--white);
    border-color: var(--white);
}

#random-btn {
    background: transparent;
    color: var(--neon-pink);
    border-color: var(--neon-pink);
}

#random-btn:hover {
    background: var(--neon-pink);
    color: var(--bg);
    box-shadow: 0 0 20px rgba(255, 45, 123, 0.4);
}

.template-selector {
    display: flex;
    align-items: center;
    gap: 10px;
    flex-wrap: wrap;
}

.template-selector label {
    font-family: var(--font-mono);
    color: var(--grey);
    font-size: 0.85rem;
}

.template-selector select {
    padding: 8px 12px;
    font-family: var(--font-mono);
    font-size: 0.85rem;
    border: 1px solid var(--border);
    border-radius: 4px;
    background: var(--bg-term);
    color: var(--white);
    cursor: pointer;
    flex: 1;
    min-width: 150px;
}

.template-selector select:focus {
    outline: none;
    border-color: var(--blue);
}

.results-panel {
    background: var(--bg-term);
    padding: 20px;
    border-radius: 4px;
    min-height: 200px;
    border: 1px solid var(--border);
    font-family: var(--font-mono);
}

.results-panel .placeholder {
    color: var(--grey);
    text-align: center;
    margin-top: 80px;
    font-size: 0.9rem;
}

.results-panel .result-item {
    display: flex;
    justify-content: space-between;
    padding: 12px 0;
    border-bottom: 1px solid var(--border);
}

.results-panel .result-item:last-child {
    border-bottom: none;
}

.results-panel .result-label {
    color: var(--grey);
}

.results-panel .result-value {
    font-weight: bold;
    color: var(--neon);
}

.results-panel .result-value.error {
    color: var(--neon-pink);
}

.log-section {
    margin-top: 10px;
}

.log-controls {
    display: flex;
    gap: 10px;
    margin-bottom: 16px;
}

#clear-log-btn, #export-log-btn {
    background: transparent;
    color: var(--grey);
    border-color: var(--border);
    padding: 8px 15px;
    font-size: 0.8rem;
}

#clear-log-btn:hover, #export-log-btn:hover {
    color: var(--white);
    border-color: var(--grey);
}

.table-wrapper {
    overflow-x: auto;
    border: 1px solid var(--border);
    border-radius: 4px;
}

#log-table {
    width: 100%;
    border-collapse: collapse;
    font-family: var(--font-mono);
    font-size: 0.8rem;
}

#log-table th, #log-table td {
    padding: 12px 14px;
    text-align: left;
    border-bottom: 1px solid var(--border);
}

#log-table th {
    background: var(--bg-term);
    color: var(--blue);
    font-weight: normal;
    text-transform: uppercase;
    letter-spacing: 1px;
    position: sticky;
    top: 0;
}

#log-table tbody tr {
    background: var(--bg-card);
}

#log-table tbody tr:hover {
    background: var(--bg-term);
}

#log-table .status-success {
    color: var(--neon);
}

#log-table .status-failed {
    color: var(--neon-pink);
}

footer {
    text-align: center;
    margin-top: 40px;
    padding: 20px;
    color: var(--grey);
    font-family: var(--font-mono);
    font-size: 0.8rem;
    border-top: 1px solid var(--border);
}

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

footer a:hover {
    color: var(--neon);
    text-decoration: underline;
}

/* Animation for solving */
@keyframes pulse {
    0%, 100% { opacity: 1; }
    50% { opacity: 0.4; }
}

.solving .sudoku-grid input {
    animation: pulse 0.6s ease-in-out infinite;
}

/* ── Benchmark section ─────────────────────────────── */
.benchmark-section {
    background: var(--bg-card);
    padding: 24px;
    border-radius: 6px;
    border: 1px solid var(--border);
}

.bench-desc {
    color: var(--grey);
    font-family: var(--font-mono);
    font-size: 0.85rem;
    margin-bottom: 16px;
}

.bench-controls {
    display: flex;
    align-items: center;
    gap: 12px;
    flex-wrap: wrap;
    margin-bottom: 16px;
}

.bench-input-group {
    display: flex;
    align-items: center;
    gap: 8px;
}

.bench-input-group label {
    font-family: var(--font-mono);
    color: var(--grey);
    font-size: 0.85rem;
}

.bench-input-group input {
    width: 100px;
    padding: 8px 10px;
    font-family: var(--font-mono);
    font-size: 0.85rem;
    border: 1px solid var(--border);
    border-radius: 4px;
    background: var(--bg-term);
    color: var(--white);
    text-align: right;
}

.bench-input-group input:focus {
    outline: none;
    border-color: var(--blue);
}

#bench-start-btn {
    background: transparent;
    color: var(--neon);
    border-color: var(--neon);
}

#bench-start-btn:hover:not(:disabled) {
    background: var(--neon);
    color: var(--bg);
    box-shadow: 0 0 20px rgba(0, 229, 255, 0.4);
}

#bench-stop-btn {
    background: transparent;
    color: var(--neon-pink);
    border-color: var(--neon-pink);
}

#bench-stop-btn:hover:not(:disabled) {
    background: var(--neon-pink);
    color: var(--bg);
    box-shadow: 0 0 20px rgba(255, 45, 123, 0.4);
}

html.light #bench-start-btn:hover:not(:disabled),
html.light #bench-stop-btn:hover:not(:disabled) {
    box-shadow: none;
}

.bench-progress-wrap {
    display: flex;
    align-items: center;
    gap: 12px;
    margin-bottom: 16px;
}

.bench-progress-bar {
    flex: 1;
    height: 10px;
    background: var(--bg-term);
    border: 1px solid var(--border);
    border-radius: 5px;
    overflow: hidden;
}

.bench-progress-fill {
    height: 100%;
    width: 0%;
    background: linear-gradient(90deg, var(--blue), var(--neon));
    transition: width 0.15s ease;
    border-radius: 5px;
}

.bench-progress-text {
    font-family: var(--font-mono);
    font-size: 0.8rem;
    color: var(--grey);
    white-space: nowrap;
    min-width: 90px;
    text-align: right;
}

.bench-stats {
    display: grid;
    grid-template-columns: repeat(auto-fill, minmax(160px, 1fr));
    gap: 12px;
}

.bench-stat {
    background: var(--bg-term);
    border: 1px solid var(--border);
    border-radius: 4px;
    padding: 14px 16px;
    display: flex;
    flex-direction: column;
    gap: 4px;
}

.bench-stat-label {
    font-family: var(--font-mono);
    color: var(--grey);
    font-size: 0.75rem;
    text-transform: uppercase;
    letter-spacing: 1px;
}

.bench-stat-value {
    font-family: var(--font-mono);
    color: var(--neon);
    font-size: 1.3rem;
    font-weight: bold;
}

/* Scrollbar styling */
::-webkit-scrollbar {
    width: 8px;
    height: 8px;
}

::-webkit-scrollbar-track {
    background: var(--bg-term);
}

::-webkit-scrollbar-thumb {
    background: var(--border);
    border-radius: 4px;
}

::-webkit-scrollbar-thumb:hover {
    background: var(--grey);
}