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

:root {
    --bg-primary: #0d1117;
    --bg-secondary: #161b22;
    --bg-tertiary: #21262d;
    --border: #30363d;
    --text-primary: #e6edf3;
    --text-secondary: #7d8590;
    --accent: #58a6ff;
    --accent-hover: #79c0ff;
    --accent-focus: #a371f7;
    --success: #3fb950;
    --danger: #f85149;
    --warning: #d29922;
    --focus-ring: 0 0 0 3px rgba(88, 166, 255, 0.4);
}

body {
    font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', 'Noto Sans', Helvetica, Arial, sans-serif;
    background: var(--bg-primary);
    color: var(--text-primary);
    line-height: 1.5;
    min-height: 100vh;
}

.container {
    max-width: 1400px;
    margin: 0 auto;
    padding: 20px;
}

header {
    text-align: center;
    margin-bottom: 24px;
}

header h1 {
    font-size: 28px;
    font-weight: 600;
    margin-bottom: 4px;
}

.subtitle {
    color: var(--text-secondary);
    font-size: 14px;
}

.subtitle a {
    color: var(--accent);
    text-decoration: none;
    border-bottom: 1px solid transparent;
    transition: border-color 0.2s;
}

.subtitle a:hover,
.subtitle a:focus {
    border-bottom-color: var(--accent);
    outline: none;
}

.subtitle a:focus-visible {
    box-shadow: var(--focus-ring);
    border-radius: 2px;
}

/* Focus styles for accessibility */
*:focus {
    outline: none;
}

*:focus-visible {
    box-shadow: var(--focus-ring);
    border-radius: 6px;
}

/* Toolbar */
.toolbar {
    display: flex;
    justify-content: space-between;
    align-items: center;
    flex-wrap: wrap;
    gap: 12px;
    background: var(--bg-secondary);
    padding: 12px 16px;
    border-radius: 8px;
    margin-bottom: 12px;
    border: 1px solid var(--border);
}

.view-modes {
    display: flex;
    gap: 8px;
}

.view-modes button,
.actions button {
    padding: 6px 14px;
    border: 1px solid var(--border);
    background: var(--bg-tertiary);
    color: var(--text-primary);
    border-radius: 6px;
    cursor: pointer;
    font-size: 13px;
    font-weight: 500;
    transition: all 0.15s;
}

.view-modes button:hover,
.actions button:hover {
    background: var(--border);
    border-color: var(--text-secondary);
}

.view-modes button:focus-visible,
.actions button:focus-visible {
    box-shadow: var(--focus-ring);
}

.view-modes button.active {
    background: var(--accent);
    border-color: var(--accent);
    color: #fff;
}

.view-modes button.active:focus-visible {
    box-shadow: 0 0 0 3px rgba(88, 166, 255, 0.3);
}

.actions {
    display: flex;
    gap: 8px;
    flex-wrap: wrap;
}

/* Options Section */
.options {
    display: flex;
    gap: 20px;
    flex-wrap: wrap;
    padding: 10px 16px;
    background: var(--bg-secondary);
    border: 1px solid var(--border);
    border-radius: 8px;
    margin-bottom: 16px;
}

.option-toggle {
    display: flex;
    align-items: center;
    gap: 8px;
    cursor: pointer;
    font-size: 13px;
    color: var(--text-secondary);
    user-select: none;
}

.option-toggle input[type="checkbox"] {
    width: 16px;
    height: 16px;
    accent-color: var(--accent);
    cursor: pointer;
}

.option-toggle input[type="checkbox"]:focus-visible {
    box-shadow: var(--focus-ring);
}

.option-toggle:hover {
    color: var(--text-primary);
}

/* Input Section */
.input-section {
    display: grid;
    grid-template-columns: 1fr 1fr;
    gap: 16px;
    margin-bottom: 16px;
}

.input-pane {
    background: var(--bg-secondary);
    border: 1px solid var(--border);
    border-radius: 8px;
    overflow: hidden;
}

.input-header {
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding: 10px 14px;
    background: var(--bg-tertiary);
    border-bottom: 1px solid var(--border);
}

.input-header label {
    font-size: 13px;
    font-weight: 600;
    color: var(--text-secondary);
    text-transform: uppercase;
    letter-spacing: 0.5px;
}

.btn-paste {
    padding: 4px 10px;
    border: 1px solid var(--border);
    background: var(--bg-secondary);
    color: var(--text-secondary);
    border-radius: 4px;
    cursor: pointer;
    font-size: 12px;
    transition: all 0.15s;
}

.btn-paste:hover {
    background: var(--border);
    color: var(--text-primary);
}

.btn-paste:focus-visible {
    box-shadow: var(--focus-ring);
}

.input-pane textarea {
    width: 100%;
    height: 180px;
    padding: 14px;
    border: none;
    background: var(--bg-secondary);
    color: var(--text-primary);
    font-family: 'SF Mono', Monaco, monospace;
    font-size: 13px;
    line-height: 1.6;
    resize: vertical;
    outline: none;
}

.input-pane textarea:focus {
    background: var(--bg-primary);
}

.input-pane textarea:focus-visible {
    box-shadow: inset var(--focus-ring);
}

.input-pane textarea::placeholder {
    color: var(--text-secondary);
}

/* Stats */
.stats {
    display: flex;
    gap: 20px;
    padding: 12px 16px;
    background: var(--bg-secondary);
    border: 1px solid var(--border);
    border-radius: 8px;
    margin-bottom: 16px;
    font-size: 13px;
}

#added-count {
    color: var(--success);
    font-weight: 600;
}

#removed-count {
    color: var(--danger);
    font-weight: 600;
}

#unchanged-count {
    color: var(--text-secondary);
}

/* Diff Output */
.diff-output {
    background: var(--bg-secondary);
    border: 1px solid var(--border);
    border-radius: 8px;
    overflow: auto;
    max-height: 80vh;
}

.diff-placeholder {
    padding: 60px 20px;
    text-align: center;
    color: var(--text-secondary);
    font-size: 14px;
}

.diff-error {
    padding: 40px 20px;
    text-align: center;
    color: var(--danger);
    font-size: 14px;
}

/* Virtualization Info */
.virtualization-info {
    display: flex;
    align-items: center;
    justify-content: center;
    gap: 12px;
    padding: 10px 16px;
    background: var(--bg-tertiary);
    border-bottom: 1px solid var(--border);
    font-size: 13px;
    color: var(--text-secondary);
    flex-wrap: wrap;
}

.virtualization-info button {
    padding: 4px 12px;
    border: 1px solid var(--border);
    background: var(--bg-secondary);
    color: var(--text-primary);
    border-radius: 4px;
    cursor: pointer;
    font-size: 12px;
    transition: all 0.15s;
}

.virtualization-info button:hover:not(:disabled) {
    background: var(--border);
}

.virtualization-info button:focus-visible {
    box-shadow: var(--focus-ring);
}

.virtualization-info button:disabled {
    opacity: 0.5;
    cursor: not-allowed;
}

/* Split View */
.diff-split {
    display: grid;
    grid-template-columns: 1fr 1fr;
}

.diff-pane {
    overflow-x: auto;
}

.diff-pane:first-child {
    border-right: 1px solid var(--border);
}

.diff-pane-header {
    padding: 10px 14px;
    background: var(--bg-tertiary);
    border-bottom: 1px solid var(--border);
    font-size: 13px;
    font-weight: 600;
    color: var(--text-secondary);
}

/* Diff Lines */
.diff-line {
    display: flex;
    font-family: 'SF Mono', Monaco, monospace;
    font-size: 13px;
    line-height: 1.6;
    min-height: 24px;
}

.diff-line.added {
    background: rgba(46, 160, 67, 0.15);
}

.diff-line.removed {
    background: rgba(248, 81, 73, 0.15);
}

.diff-line.unchanged {
    background: transparent;
}

.line-number {
    width: 50px;
    padding: 2px 10px;
    text-align: right;
    color: var(--text-secondary);
    background: var(--bg-tertiary);
    border-right: 1px solid var(--border);
    user-select: none;
    flex-shrink: 0;
}

.line-content {
    padding: 2px 10px;
    white-space: pre;
    overflow-x: auto;
    flex: 1;
}

.diff-line.added .line-content {
    background: rgba(46, 160, 67, 0.1);
}

.diff-line.removed .line-content {
    background: rgba(248, 81, 73, 0.1);
}

.line-marker {
    width: 20px;
    padding: 2px 6px;
    color: var(--text-secondary);
    user-select: none;
    flex-shrink: 0;
}

.diff-line.added .line-marker {
    color: var(--success);
}

.diff-line.removed .line-marker {
    color: var(--danger);
}

/* Inline View */
.diff-inline .diff-line {
    border-left: 3px solid transparent;
}

.diff-inline .diff-line.added {
    border-left-color: var(--success);
}

.diff-inline .diff-line.removed {
    border-left-color: var(--danger);
}

/* Empty state */
.diff-empty {
    padding: 40px;
    text-align: center;
    color: var(--text-secondary);
}

/* Toast */
.toast {
    position: fixed;
    bottom: 20px;
    left: 50%;
    transform: translateX(-50%) translateY(100px);
    background: var(--bg-tertiary);
    color: var(--text-primary);
    padding: 12px 24px;
    border-radius: 8px;
    border: 1px solid var(--border);
    box-shadow: 0 4px 12px rgba(0, 0, 0, 0.3);
    opacity: 0;
    transition: all 0.3s;
    z-index: 1000;
    font-size: 14px;
}

.toast.show {
    transform: translateX(-50%) translateY(0);
    opacity: 1;
}

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

/* High contrast mode support */
@media (prefers-contrast: high) {
    :root {
        --border: #6e7681;
        --text-secondary: #c9d1d9;
    }
    
    .diff-line.added {
        background: rgba(46, 160, 67, 0.3);
    }
    
    .diff-line.removed {
        background: rgba(248, 81, 73, 0.3);
    }
}

/* Responsive */
@media (max-width: 900px) {
    .input-section {
        grid-template-columns: 1fr;
    }
    
    .diff-split {
        grid-template-columns: 1fr;
    }
    
    .diff-pane:first-child {
        border-right: none;
        border-bottom: 1px solid var(--border);
    }
    
    .toolbar {
        flex-direction: column;
        align-items: stretch;
    }
    
    .actions {
        justify-content: center;
    }
    
    .options {
        justify-content: center;
    }
}

/* Print styles */
@media print {
    .toolbar,
    .options,
    .input-section,
    .stats,
    .toast {
        display: none !important;
    }
    
    .diff-output {
        border: 1px solid #000;
        max-height: none;
    }
}