:root {
    --primary-color: #007AFF;
    /* iOS Blue */
    --primary-hover: #0056b3;
    --background-color: #f2f2f7;
    /* iOS System Gray 6 */
    --card-bg: #ffffff;
    --text-color: #1c1c1e;
    --text-muted: #8e8e93;
    --border-color: #d1d1d6;
    --radius-sm: 8px;
    --radius-md: 12px;
    --radius-lg: 16px;
    --radius-xl: 24px;
    --font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
}

body {
    font-family: var(--font-family);
    max-width: 1000px;
    margin: 0 auto;
    padding: 20px;
    background-color: var(--background-color);
    color: var(--text-color);
    line-height: 1.5;
    padding-bottom: 120px;
    /* Space for sticky footer */
}

h1 {
    text-align: center;
    margin-bottom: 2rem;
    font-weight: 700;
}

p {
    text-align: center;
    margin-bottom: 1rem;
    color: var(--text-muted);
}

/* Drop Zone */
#dropZone {
    border: 2px dashed #aeaeb2;
    border-radius: var(--radius-xl);
    width: 100%;
    height: 180px;
    display: flex;
    justify-content: center;
    align-items: center;
    margin: 20px 0 40px 0;
    background-color: var(--card-bg);
    transition: all 0.3s ease;
    cursor: pointer;
    font-weight: 600;
    color: #8e8e93;
    font-size: 1.1rem;
}

#dropZone:hover {
    border-color: var(--primary-color);
    background-color: #e4eaff;
    color: var(--primary-color);
}

/* Options Panel */
.options-container {
    background: var(--card-bg);
    padding: 24px;
    border-radius: var(--radius-lg);
    box-shadow: 0 2px 10px rgba(0, 0, 0, 0.03);
    margin-bottom: 30px;
    display: grid;
    grid-template-columns: repeat(auto-fill, minmax(250px, 1fr));
    gap: 16px;
}

.checkbox-container {
    display: flex;
    align-items: center;
    gap: 12px;
    cursor: pointer;
    user-select: none;
}

.checkbox-container input[type="checkbox"] {
    accent-color: var(--primary-color);
    width: 20px;
    height: 20px;
    cursor: pointer;
}

.checkbox-container label {
    cursor: pointer;
    font-size: 0.95rem;
    color: var(--text-color);
}

/* Gallery / Grid Layout (iPhone Style) */
#pngGridControls {
    display: flex;
    justify-content: space-between;
    align-items: center;
    margin-bottom: 15px;
    padding: 0 10px;
}

#pngGrid {
    display: grid;
    /* Use CSS variable for efficient resizing without DOM reconstruction */
    --grid-item-size: 130px;
    /* Default matches approx 30% scale */
    grid-template-columns: repeat(auto-fill, minmax(var(--grid-item-size), 1fr));
    gap: 1px;
    /* Tighter, more precise gap like native iOS Photos */
    margin-bottom: 40px;
    background-color: var(--card-bg);
    /* Ensure contrast */
    padding: 1px;
    /* Optional border-like effect */
    border-radius: var(--radius-sm);
}

.png-node {
    position: relative;
    background-color: #fff;
    aspect-ratio: 1 / 1;
    /* Perfect square */
    overflow: hidden;
    cursor: pointer;
    transition: transform 0.2s;
}

.png-node img {
    width: 100%;
    height: 100%;
    object-fit: cover;
    /* Fill the square */
    transition: opacity 0.2s;
}

.png-node.checkerboard-bg img {
    /* If checkerboard is desired, we might want 'contain' to see transparency? 
       But 'iPhone style' implies 'cover'. User asked for checkerboard previously.
       Let's stick to cover for aesthetics, but maybe add a toggle for 'fit' if needed later.
       For now, object-fit: cover is the most "Library" look.
    */
    background-image: linear-gradient(45deg, #e5e5ea 25%, transparent 25%),
        linear-gradient(-45deg, #e5e5ea 25%, transparent 25%),
        linear-gradient(45deg, transparent 75%, #e5e5ea 75%),
        linear-gradient(-45deg, transparent 75%, #e5e5ea 75%);
    background-size: 8px 8px;
    background-position: 0 0, 0 4px, 4px -4px, -4px 0px;
}

/* Selection State */
.png-node.selected img {
    opacity: 0.8;
}

.png-node.selected::after {
    content: '';
    position: absolute;
    inset: 0;
    border: 3px solid var(--primary-color);
    box-sizing: border-box;
    z-index: 2;
}

/* Selection Checkmark Overlay */
.selection-indicator {
    position: absolute;
    bottom: 6px;
    right: 6px;
    width: 22px;
    height: 22px;
    border-radius: 50%;
    border: 2px solid rgba(255, 255, 255, 0.8);
    background-color: rgba(0, 0, 0, 0.1);
    z-index: 3;
    transition: all 0.2s ease;
    pointer-events: none;
    /* Clicking the cell triggers it */
}

.png-node.selected .selection-indicator {
    background-color: var(--primary-color);
    border-color: var(--primary-color);
    box-shadow: 0 2px 5px rgba(0, 0, 0, 0.2);
}

.png-node.selected .selection-indicator::before {
    content: '✓';
    position: absolute;
    top: 50%;
    left: 50%;
    transform: translate(-50%, -50%);
    color: white;
    font-size: 12px;
    font-weight: bold;
}

/* Hide labels in grid view to act like iPhone library */
.png-node-label {
    display: none;
}

/* File Size Badge - Make it subtle or hide in gallery view? 
   Let's keep it very minimal or maybe hide it for the clean look.
   User asked for "iPhone library" look which has NO text overlays usually.
   I'll hide it by default in this mode, or maybe show on hover.
*/
.png-node-size {
    display: none;
}

/* List View (for non-image files) */
.category h3 {
    margin-top: 30px;
    font-size: 1.2rem;
    color: var(--text-color);
    border-bottom: 1px solid var(--border-color);
    padding-bottom: 10px;
    margin-bottom: 15px;
    display: flex;
    align-items: center;
    justify-content: space-between;
}

#fileList ul {
    list-style: none;
    padding: 0;
}

#fileList li {
    background: var(--card-bg);
    border-bottom: 1px solid var(--border-color);
    padding: 12px 16px;
    display: flex;
    align-items: center;
}

#fileList li:first-child {
    border-top-left-radius: var(--radius-md);
    border-top-right-radius: var(--radius-md);
}

#fileList li:last-child {
    border-bottom-left-radius: var(--radius-md);
    border-bottom-right-radius: var(--radius-md);
    border-bottom: none;
}

.file-checkbox {
    margin-right: 15px;
    width: 20px;
    height: 20px;
    accent-color: var(--primary-color);
}

#fileList li a {
    color: var(--text-color);
    text-decoration: none;
    flex-grow: 1;
    white-space: nowrap;
    overflow: hidden;
    text-overflow: ellipsis;
}

/* Buttons */
button {
    background-color: #e5e5ea;
    color: var(--primary-color);
    border: none;
    padding: 8px 16px;
    border-radius: 18px;
    font-weight: 600;
    cursor: pointer;
    transition: background 0.2s;
}

button:hover {
    background-color: #d1d1d6;
}

.download-all button {
    background-color: var(--primary-color);
    color: white;
    padding: 12px 24px;
    font-size: 1.1rem;
}

.download-all button:hover {
    background-color: var(--primary-hover);
}

/* Sticky Selection Bar */
#selectionBar {
    position: fixed;
    bottom: 30px;
    left: 50%;
    transform: translateX(-50%) translateY(150%);
    background-color: rgba(28, 28, 30, 0.9);
    /* Dark translucent */
    backdrop-filter: blur(10px);
    color: white;
    padding: 16px 32px;
    border-radius: 40px;
    box-shadow: 0 10px 30px rgba(0, 0, 0, 0.3);
    display: flex;
    align-items: center;
    gap: 20px;
    z-index: 2000;
    transition: transform 0.4s cubic-bezier(0.19, 1, 0.22, 1);
    width: fit-content;
    min-width: 320px;
    justify-content: space-between;
}

#selectionBar.visible {
    transform: translateX(-50%) translateY(0);
}

#selectionCount {
    font-weight: 600;
}

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

#clearSelectionBtn {
    background: rgba(255, 255, 255, 0.2);
    color: white;
}