:root {
    --color-bg: #f6f7f9;
    --color-surface: #ffffff;
    --color-text: #1a1d23;
    --color-text-muted: #6b7280;
    --color-border: #e5e7eb;
    --color-border-strong: #d1d5db;
    --color-primary: #5b6cff;
    --color-primary-hover: #4654e0;
    --color-primary-disabled: #b8c0ff;
    --color-danger: #dc2626;
    --color-danger-bg: #fee2e2;
    --color-success: #10b981;

    --radius-sm: 6px;
    --radius-md: 10px;
    --radius-lg: 16px;

    --shadow-sm: 0 1px 2px rgba(15, 23, 42, 0.04);
    --shadow-md: 0 4px 12px rgba(15, 23, 42, 0.06);

    --space-xs: 0.5rem;
    --space-sm: 0.75rem;
    --space-md: 1rem;
    --space-lg: 1.5rem;
    --space-xl: 2rem;

    --font-sans: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, "Helvetica Neue", Arial, sans-serif;

    --transition: 150ms ease;
}

@media (prefers-color-scheme: dark) {
    :root {
        --color-bg: #0f1115;
        --color-surface: #1a1d23;
        --color-text: #e5e7eb;
        --color-text-muted: #9ca3af;
        --color-border: #2a2f37;
        --color-border-strong: #3a414b;
        --color-primary: #7c8cff;
        --color-primary-hover: #93a0ff;
        --color-primary-disabled: #3a4170;
        --color-danger: #f87171;
        --color-danger-bg: #3b1f1f;
    }
}

* { box-sizing: border-box; }

html, body {
    margin: 0;
    padding: 0;
    background: var(--color-bg);
    color: var(--color-text);
    font-family: var(--font-sans);
    font-size: 16px;
    line-height: 1.5;
    -webkit-font-smoothing: antialiased;
}

.visually-hidden {
    position: absolute;
    width: 1px;
    height: 1px;
    padding: 0;
    margin: -1px;
    overflow: hidden;
    clip: rect(0, 0, 0, 0);
    white-space: nowrap;
    border: 0;
}

.container {
    max-width: 760px;
    margin: 0 auto;
    padding: var(--space-xl) var(--space-md);
}

.header {
    text-align: center;
    margin-bottom: var(--space-xl);
}

.header h1 {
    margin: 0 0 var(--space-xs);
    font-size: 2.25rem;
    letter-spacing: -0.02em;
}

.subtitle {
    margin: 0;
    color: var(--color-text-muted);
}

.card {
    background: var(--color-surface);
    border: 1px solid var(--color-border);
    border-radius: var(--radius-lg);
    padding: var(--space-lg);
    margin-bottom: var(--space-md);
    box-shadow: var(--shadow-sm);
}

.card h2 {
    margin: 0 0 var(--space-md);
    font-size: 1.05rem;
    font-weight: 600;
    color: var(--color-text-muted);
    letter-spacing: 0.02em;
    text-transform: uppercase;
}

/* Drop zone */
.drop-zone {
    display: flex;
    flex-direction: column;
    align-items: center;
    justify-content: center;
    gap: var(--space-xs);
    padding: var(--space-xl) var(--space-md);
    border: 2px dashed var(--color-border-strong);
    border-radius: var(--radius-md);
    cursor: pointer;
    transition: border-color var(--transition), background var(--transition);
    text-align: center;
}

.drop-zone:hover,
.drop-zone:focus-within {
    border-color: var(--color-primary);
    background: rgba(91, 108, 255, 0.04);
}

.drop-zone--active {
    border-color: var(--color-primary);
    background: rgba(91, 108, 255, 0.08);
}

.drop-zone__icon {
    color: var(--color-text-muted);
}

.drop-zone__text {
    font-weight: 500;
}

.drop-zone__hint {
    color: var(--color-text-muted);
    font-size: 0.875rem;
}

/* Frame list */
.frame-list {
    display: grid;
    grid-template-columns: repeat(auto-fill, minmax(80px, 1fr));
    gap: var(--space-xs);
    margin-top: var(--space-md);
}

.frame-list:empty { margin-top: 0; }

.frame {
    position: relative;
    aspect-ratio: 1 / 1;
    border-radius: var(--radius-sm);
    overflow: hidden;
    background: var(--color-bg);
    border: 1px solid var(--color-border);
}

.frame img {
    width: 100%;
    height: 100%;
    object-fit: cover;
    display: block;
}

.frame__index {
    position: absolute;
    top: 4px;
    left: 4px;
    background: rgba(0, 0, 0, 0.65);
    color: white;
    font-size: 0.75rem;
    font-weight: 600;
    padding: 2px 6px;
    border-radius: var(--radius-sm);
}

.frame__remove {
    position: absolute;
    top: 4px;
    right: 4px;
    width: 22px;
    height: 22px;
    padding: 0;
    border: 0;
    border-radius: 50%;
    background: rgba(0, 0, 0, 0.65);
    color: white;
    font-size: 1rem;
    line-height: 1;
    cursor: pointer;
    display: flex;
    align-items: center;
    justify-content: center;
    transition: background var(--transition);
}

.frame__remove:hover { background: var(--color-danger); }

.frame-actions {
    display: flex;
    align-items: center;
    justify-content: space-between;
    margin-top: var(--space-md);
    padding-top: var(--space-md);
    border-top: 1px solid var(--color-border);
}

.frame-count {
    color: var(--color-text-muted);
    font-size: 0.875rem;
}

/* Controls */
.controls {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(220px, 1fr));
    gap: var(--space-md);
}

.control {
    display: flex;
    flex-direction: column;
    gap: var(--space-xs);
}

.control label {
    font-weight: 500;
    font-size: 0.9rem;
    display: flex;
    flex-direction: column;
    gap: 2px;
}

.control__hint {
    color: var(--color-text-muted);
    font-size: 0.8rem;
    font-weight: 400;
}

.control input[type="number"],
.control select {
    padding: var(--space-xs) var(--space-sm);
    border: 1px solid var(--color-border-strong);
    border-radius: var(--radius-sm);
    background: var(--color-surface);
    color: var(--color-text);
    font-size: 1rem;
    font-family: inherit;
    transition: border-color var(--transition), box-shadow var(--transition);
}

.control input[type="number"]:focus,
.control select:focus {
    outline: none;
    border-color: var(--color-primary);
    box-shadow: 0 0 0 3px rgba(91, 108, 255, 0.15);
}

.range-row {
    display: flex;
    align-items: center;
    gap: var(--space-sm);
}

.range-row input[type="range"] {
    flex: 1;
    accent-color: var(--color-primary);
}

.range-row output {
    min-width: 2ch;
    text-align: right;
    font-variant-numeric: tabular-nums;
    color: var(--color-text-muted);
}

/* Buttons */
.btn {
    display: inline-flex;
    align-items: center;
    justify-content: center;
    gap: var(--space-xs);
    padding: 0.7rem 1.25rem;
    border: 0;
    border-radius: var(--radius-sm);
    font-size: 1rem;
    font-weight: 500;
    font-family: inherit;
    cursor: pointer;
    text-decoration: none;
    transition: background var(--transition), color var(--transition), transform var(--transition);
}

.btn:active { transform: translateY(1px); }

.btn--primary {
    background: var(--color-primary);
    color: white;
    width: 100%;
}

.btn--primary:hover:not(:disabled) { background: var(--color-primary-hover); }

.btn--primary:disabled {
    background: var(--color-primary-disabled);
    cursor: not-allowed;
}

.btn--ghost {
    background: transparent;
    color: var(--color-text-muted);
    padding: 0.4rem 0.75rem;
    font-size: 0.875rem;
}

.btn--ghost:hover {
    color: var(--color-danger);
    background: var(--color-danger-bg);
}

/* Status / Progress */
.status {
    display: flex;
    align-items: center;
    gap: var(--space-md);
    margin-top: var(--space-md);
    padding: var(--space-md);
    background: var(--color-bg);
    border-radius: var(--radius-md);
}

.status__text {
    flex: 1;
    display: flex;
    flex-direction: column;
    gap: var(--space-xs);
    font-size: 0.9rem;
    color: var(--color-text-muted);
}

.spinner {
    width: 24px;
    height: 24px;
    border: 3px solid var(--color-border-strong);
    border-top-color: var(--color-primary);
    border-radius: 50%;
    animation: spin 0.8s linear infinite;
    flex-shrink: 0;
}

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

.progress {
    width: 100%;
    height: 6px;
    background: var(--color-border);
    border-radius: 999px;
    overflow: hidden;
}

.progress__bar {
    height: 100%;
    width: 0;
    background: var(--color-primary);
    border-radius: 999px;
    transition: width 200ms ease;
}

/* Error */
.error {
    margin-top: var(--space-md);
    padding: var(--space-sm) var(--space-md);
    background: var(--color-danger-bg);
    color: var(--color-danger);
    border-radius: var(--radius-sm);
    font-size: 0.9rem;
}

/* Output */
.output {
    margin-top: var(--space-md);
    padding-top: var(--space-md);
    border-top: 1px solid var(--color-border);
    text-align: center;
}

.output h3 {
    margin: 0 0 var(--space-md);
    font-size: 1.1rem;
}

.output img {
    max-width: 100%;
    max-height: 400px;
    border-radius: var(--radius-md);
    border: 1px solid var(--color-border);
    background:
        repeating-conic-gradient(var(--color-bg) 0% 25%, var(--color-surface) 0% 50%) 50% / 20px 20px;
}

.output__meta {
    margin: var(--space-sm) 0;
    color: var(--color-text-muted);
    font-size: 0.875rem;
}

/* Footer */
.footer {
    text-align: center;
    color: var(--color-text-muted);
    font-size: 0.875rem;
    margin-top: var(--space-xl);
}

/* Responsive */
@media (max-width: 480px) {
    .header h1 { font-size: 1.75rem; }
    .card { padding: var(--space-md); }
    .container { padding: var(--space-md) var(--space-sm); }
}