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

:root {
    --primary-color: #2563eb;
    --primary-hover: #1d4ed8;
    --bg-dark: #1a1a2e;
    --bg-panel: #16213e;
    --text-primary: #e8e8e8;
    --text-secondary: #a0a0a0;
    --border-color: #2a2a4a;
    --success-color: #22c55e;
    --warning-color: #f59e0b;
}

body {
    font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, sans-serif;
    background: var(--bg-dark);
    color: var(--text-primary);
    min-height: 100vh;
    overflow: hidden;
}

#app {
    display: flex;
    flex-direction: column;
    height: 100vh;
}

header {
    background: var(--bg-panel);
    padding: 1rem 2rem;
    border-bottom: 1px solid var(--border-color);
    text-align: center;
}

header h1 {
    font-size: 1.5rem;
    font-weight: 600;
    margin-bottom: 0.25rem;
}

header .subtitle {
    color: var(--text-secondary);
    font-size: 0.875rem;
}

main {
    display: flex;
    flex: 1;
    overflow: hidden;
}

#viewer-container {
    flex: 1;
    position: relative;
    background: linear-gradient(135deg, #0f0f1a 0%, #1a1a2e 100%);
}

#three-canvas {
    width: 100%;
    height: 100%;
    display: block;
}

#loading-overlay {
    position: absolute;
    top: 0;
    left: 0;
    right: 0;
    bottom: 0;
    background: rgba(26, 26, 46, 0.95);
    display: flex;
    flex-direction: column;
    align-items: center;
    justify-content: center;
    z-index: 100;
    transition: opacity 0.3s ease;
}

#loading-overlay.hidden {
    opacity: 0;
    pointer-events: none;
}

.spinner {
    width: 50px;
    height: 50px;
    border: 3px solid var(--border-color);
    border-top-color: var(--primary-color);
    border-radius: 50%;
    animation: spin 1s linear infinite;
}

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

#loading-overlay p {
    margin-top: 1rem;
    color: var(--text-secondary);
}

#controls-panel {
    width: 400px;
    background: var(--bg-panel);
    border-left: 1px solid var(--border-color);
    overflow-y: auto;
    display: flex;
    flex-direction: column;
    gap: 1rem;
    padding: 1.5rem;
}

#controls-panel section {
    background: rgba(255, 255, 255, 0.02);
    border: 1px solid var(--border-color);
    border-radius: 8px;
    padding: 1rem;
}

#controls-panel h2 {
    font-size: 1.25rem;
    margin-bottom: 0.5rem;
    color: var(--primary-color);
}

#controls-panel h3 {
    font-size: 1.1rem;
    margin-bottom: 0.75rem;
}

#controls-panel h4 {
    font-size: 0.875rem;
    text-transform: uppercase;
    letter-spacing: 0.05em;
    color: var(--text-secondary);
    margin-bottom: 0.75rem;
}

#step-description {
    min-height: 150px;
    color: var(--text-secondary);
    line-height: 1.6;
    font-size: 0.9rem;
}

#navigation {
    display: flex;
    gap: 0.75rem;
}

#navigation button {
    flex: 1;
    padding: 0.75rem 1rem;
    font-size: 1rem;
    font-weight: 500;
    border: none;
    border-radius: 6px;
    cursor: pointer;
    transition: all 0.2s ease;
}

#btn-prev {
    background: var(--border-color);
    color: var(--text-primary);
}

#btn-prev:hover:not(:disabled) {
    background: #3a3a5a;
}

#btn-next {
    background: var(--primary-color);
    color: white;
}

#btn-next:hover:not(:disabled) {
    background: var(--primary-hover);
}

#btn-complete-model {
    background: var(--success-color);
    color: white;
}

#btn-complete-model:hover {
    background: #16a34a;
}

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

#view-controls .control-group {
    display: flex;
    gap: 0.5rem;
    margin-bottom: 0.75rem;
}

#view-controls .control-group:last-child {
    margin-bottom: 0;
}

#view-controls button {
    flex: 1;
    padding: 0.5rem;
    font-size: 0.85rem;
    background: var(--border-color);
    border: none;
    border-radius: 4px;
    color: var(--text-primary);
    cursor: pointer;
    transition: background 0.2s ease;
}

#view-controls button:hover {
    background: #3a3a5a;
}

#view-controls button.active {
    background: var(--primary-color);
}

#view-controls label {
    display: flex;
    align-items: center;
    gap: 0.5rem;
    cursor: pointer;
    font-size: 0.9rem;
    color: var(--text-secondary);
}

#view-controls input[type="checkbox"] {
    width: 16px;
    height: 16px;
    accent-color: var(--primary-color);
}

#parts-overview {
    list-style: none;
    max-height: 200px;
    overflow-y: auto;
}

#parts-overview li {
    padding: 0.5rem;
    margin-bottom: 0.25rem;
    border-radius: 4px;
    font-size: 0.85rem;
    color: var(--text-secondary);
    display: flex;
    align-items: center;
    gap: 0.5rem;
    transition: all 0.2s ease;
}

#parts-overview li::before {
    content: '';
    width: 8px;
    height: 8px;
    border-radius: 50%;
    background: var(--border-color);
    flex-shrink: 0;
}

#parts-overview li.assembled::before {
    background: var(--success-color);
}

#parts-overview li.current::before {
    background: var(--warning-color);
}

#parts-overview li.current {
    background: rgba(245, 158, 11, 0.1);
    color: var(--text-primary);
}

#instructions ul {
    list-style: none;
}

#instructions li {
    padding: 0.35rem 0;
    font-size: 0.85rem;
    color: var(--text-secondary);
}

#instructions strong {
    color: var(--text-primary);
}

footer {
    background: var(--bg-panel);
    padding: 0.75rem;
    text-align: center;
    font-size: 0.8rem;
    color: var(--text-secondary);
    border-top: 1px solid var(--border-color);
}

/* Responsive adjustments */
@media (max-width: 900px) {
    main {
        flex-direction: column;
    }

    #viewer-container {
        height: 50vh;
    }

    #controls-panel {
        width: 100%;
        height: 50vh;
        border-left: none;
        border-top: 1px solid var(--border-color);
    }
}

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

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

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

::-webkit-scrollbar-thumb:hover {
    background: #3a3a5a;
}