#lens-ray-tracer-app {
    --billy-orange: #F5A623; 
    --billy-dark: #333; 
    --billy-blue: #008080; 
    --bg-light: #f9f9f9; 
    --slate-200: #e2e8f0;
    --slate-500: #64748b;
    --slate-800: #1e293b;
    --red-500: #ef4444;
    --green-500: #22c55e;
    font-family: 'Inter', 'Segoe UI', sans-serif;
    -webkit-font-smoothing: antialiased;
    width: 100%;
}

#lens-ray-tracer-app * { box-sizing: border-box; }

#lens-ray-tracer-app .billy-notes-wrapper {
    line-height: 1.6; 
    color: #333; 
    width: 100%; 
    max-width: 800px;
    margin: 0 auto; 
    padding: 20px; 
    background: transparent;
    min-height: 850px; /* Prevents layout shift */
}

#lens-ray-tracer-app .app-header { margin-bottom: 20px; }
#lens-ray-tracer-app .main-title { 
    color: var(--billy-blue); 
    border-bottom: 3px solid var(--billy-orange); 
    padding-bottom: 10px; 
    font-size: 2em; 
    text-align: center; 
    margin-bottom: 20px; 
    margin-top: 0; 
    font-weight: bold;
}
#lens-ray-tracer-app .subtitle { text-align: center; margin-bottom: 20px; }

#lens-ray-tracer-app .zh-text { color: #666; font-size: 0.9em; display: block; margin-top: 4px; font-weight: normal; }
#lens-ray-tracer-app .inline-zh { display: inline; font-size: 0.85em; }

#lens-ray-tracer-app .note-card { 
    background: var(--bg-light); 
    border-radius: 12px; 
    padding: 0; 
    margin: 20px 0; 
    box-shadow: 0 4px 15px rgba(0,0,0,0.05); 
    border-top: 4px solid var(--billy-blue); 
    overflow: hidden;
}

#lens-ray-tracer-app .card-header {
    padding: 20px 25px;
    border-bottom: 1px solid var(--slate-200);
    background: #fff;
}

#lens-ray-tracer-app .diagram-container {
    position: relative;
    width: 100%;
    background: #0f172a;
    border-bottom: 1px solid var(--slate-200);
    padding: 0;
    line-height: 0;
    margin: 0;
}
#lens-ray-tracer-app canvas#simCanvas {
    display: block;
    width: 100%;
    height: auto;
    cursor: crosshair;
}

#lens-ray-tracer-app .sliders-wrapper {
    padding: 25px;
    background: #fff;
    border-bottom: 1px solid var(--slate-200);
    display: grid;
    grid-template-columns: 1fr 1fr;
    gap: 20px;
    margin: 0;
}
#lens-ray-tracer-app fieldset { border: none; padding: 0; margin: 0; }
#lens-ray-tracer-app .slider-group { display: flex; flex-direction: column; gap: 8px; }
#lens-ray-tracer-app .slider-header {
    display: flex; justify-content: space-between; align-items: center;
    font-weight: bold; font-size: 0.9rem; color: var(--slate-800); margin-bottom: 0.5rem;
}
#lens-ray-tracer-app .val-badge {
    background: var(--bg-light); border: 1px solid var(--slate-200);
    padding: 2px 6px; border-radius: 4px; font-family: 'JetBrains Mono', monospace; font-size: 0.85rem;
}
#lens-ray-tracer-app .val-badge.focal { color: #ef4444; border-color: #fecaca; background: #fef2f2; }
#lens-ray-tracer-app .val-badge.dist { color: #3b82f6; border-color: #bfdbfe; background: #eff6ff; }
#lens-ray-tracer-app .val-badge.height { color: #8b5cf6; border-color: #ddd6fe; background: #f5f3ff; }

#lens-ray-tracer-app input[type=range] {
    -webkit-appearance: none; width: 100%; background: transparent; margin: 8px 0;
}
#lens-ray-tracer-app input[type=range]::-webkit-slider-thumb {
    -webkit-appearance: none; height: 18px; width: 18px; border-radius: 50%;
    background: var(--billy-blue); cursor: pointer; margin-top: -6px; 
    box-shadow: 0 2px 4px rgba(0,0,0,0.2); border: 2px solid white;
}
#lens-ray-tracer-app .slider-focal::-webkit-slider-thumb { background: #ef4444 !important; }
#lens-ray-tracer-app .slider-dist::-webkit-slider-thumb { background: #3b82f6 !important; }
#lens-ray-tracer-app .slider-height::-webkit-slider-thumb { background: #8b5cf6 !important; }

#lens-ray-tracer-app input[type=range]::-webkit-slider-runnable-track {
    width: 100%; height: 6px; cursor: pointer; background: var(--slate-200); border-radius: 3px;
}

#lens-ray-tracer-app .controls {
    padding: 25px; display: grid; grid-template-columns: 1fr 1fr; gap: 20px; background: #fff; margin: 0;
}

#lens-ray-tracer-app .btn-reset {
    background: white; border: 2px solid var(--billy-blue); color: var(--billy-blue);
    padding: 15px; border-radius: 12px; font-weight: 700; font-size: 1rem;
    cursor: pointer; transition: all 0.2s; display: flex; flex-direction: column;
    align-items: center; justify-content: center; gap: 4px;
}
#lens-ray-tracer-app .btn-reset:hover { background: #f0f8f8; transform: translateY(-2px); }
#lens-ray-tracer-app .btn-reset:active { transform: scale(0.98); }
#lens-ray-tracer-app .btn-reset .zh-text { color: var(--billy-blue); margin-top: 0; }

#lens-ray-tracer-app .info-box {
    margin: 0 25px 25px 25px; padding: 20px; background: #fffbf0;
    border-left: 5px solid var(--billy-orange); border-radius: 0 8px 8px 0;
    color: #333; font-size: 0.95rem;
}

@media (max-width: 600px) {
    #lens-ray-tracer-app .billy-notes-wrapper { padding: 12px; }
    #lens-ray-tracer-app .card-header { padding: 15px; }
    #lens-ray-tracer-app .sliders-wrapper { grid-template-columns: 1fr; gap: 15px; padding: 20px; }
    #lens-ray-tracer-app .controls { grid-template-columns: 1fr; gap: 15px; padding: 20px; }
    #lens-ray-tracer-app .info-box { margin: 0 15px 20px 15px; padding: 15px; }
}