:root {
            --bg-color: #ffffff;
            --text-color: #333333;
            --container-bg: #f9f9f9;
            --border-color: #e0e0e0;
            --primary-color: #007bff;
            --primary-hover: #0056b3;
            --input-bg: #ffffff;
            --input-border: #ccc;
            --header-height: 50px;
            --footer-height: 90px;
        }

        html,
        body {
            margin: 0;
        }

        body {
            font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, "Helvetica Neue", Arial, sans-serif;
            background-color: var(--bg-color);
            color: var(--text-color);
        }

        .icon {
            width: 1em;
            height: 1em;
            fill: currentColor;
            flex: none;
            vertical-align: -0.125em;
        }

        .above-the-fold {
            display: flex;
            flex-direction: column;
        }

        .top-bar {
            height: var(--header-height);
            display: flex;
            justify-content: space-between;
            align-items: center;
            padding: 0 20px;
            background-color: var(--primary-color);
            color: white;
            flex-shrink: 0;
        }

        .top-bar a,
        .top-bar button {
            color: white;
            text-decoration: none;
            background: none;
            border: none;
            cursor: pointer;
            font-size: 16px;
            padding: 8px 12px;
            border-radius: 5px;
            transition: background-color 0.3s;
        }

        .top-bar a:hover,
        .top-bar button:hover {
            background-color: var(--primary-hover);
        }

        .container {
            max-width: 800px;
            margin: 20px auto;
            padding: 20px;
            background-color: var(--container-bg);
            border-radius: 8px;
            box-shadow: 0 2px 10px rgba(0, 0, 0, 0.1);
            flex-grow: 1;
            display: flex;
            flex-direction: column;
        }

        h1,
        h2 {
            text-align: center;
            color: var(--text-color);
            flex-shrink: 0;
        }

        h1 {
            font-size: 2em;
            margin-bottom: 10px;
            margin-top: 0;
        }

        h2 {
            font-size: 1.2em;
            font-weight: normal;
            color: #666;
            margin-top: 0;
            margin-bottom: 20px;
        }

        .color-grid {
            display: grid;
            grid-template-columns: repeat(20, 1fr);
            gap: 2px;
            height: 40vh; /* Set a responsive height */
            --grid-alpha: 1.0;
            transition: opacity 0.2s ease;
        }

        .gray-scale {
            margin: 15px auto;
            max-width: 400px;
            width: 100%;
            height: 25px;
            cursor: pointer;
            border-radius: 3px;
            background: linear-gradient(to right, #ffffff, #000000);
            border: 1px solid var(--border-color);
            flex-shrink: 0;
        }

        .color-box {
            width: 100%;
            height: 100%;
            cursor: pointer;
            border-radius: 3px;
            transition: transform 0.1s;
            background-color: rgba(var(--rgb, 255, 255, 255), var(--grid-alpha));
        }

        .color-box:hover {
            transform: scale(1.1);
            border: 1px solid var(--text-color);
            z-index: 10;
            position: relative;
        }

        .controls {
            display: flex;
            justify-content: center;
            align-items: center;
            gap: 25px;
            margin-top: 15px;
            flex-shrink: 0;
        }

        #color-preview {
            width: 88px;
            height: 88px;
            border: 1px solid var(--border-color);
            border-radius: 5px;
            background-image: linear-gradient(45deg, #ccc 25%, transparent 25%), linear-gradient(-45deg, #ccc 25%, transparent 25%), linear-gradient(45deg, transparent 75%, #ccc 75%), linear-gradient(-45deg, transparent 75%, #ccc 75%);
            background-size: 16px 16px;
            background-position: 0 0, 0 8px, 8px -8px, -8px 0px;
            position: relative;
            overflow: hidden;
        }

        #color-preview::before {
            content: '';
            position: absolute;
            top: 0; right: 0; bottom: 0; left: 0;
            background-color: var(--preview-color, #fff);
        }

        .color-values {
            display: flex;
            flex-direction: column;
            gap: 5px;
        }

        .color-value-row {
            display: flex;
            align-items: center;
            gap: 8px;
        }

        .color-value-row label {
            font-weight: bold;
            font-size: 14px;
            width: 35px;
            color: #555;
        }

        .color-value-row input {
            font-family: "SF Mono", "Consolas", "Menlo", monospace;
            padding: 5px 8px;
            font-size: 14px;
            border: 1px solid var(--input-border);
            border-radius: 5px;
            width: 170px;
            height: 28px;
            box-sizing: border-box;
            background-color: var(--input-bg);
            color: var(--text-color);
        }

        .color-value-row input[readonly] {
            background-color: #f1f1f1;
            cursor: default;
            color: #555;
        }

        .copy-btn {
            background: none;
            border: 1px solid transparent;
            cursor: pointer;
            font-size: 15px;
            padding: 4px;
            border-radius: 5px;
            color: #777;
            transition: background-color 0.2s, color 0.2s;
        }

        .copy-btn:hover {
            background-color: #e9e9e9;
            color: #000;
        }

        .preview-container {
            position: relative;
        }

        .eyedropper-btn {
            position: absolute;
            top: 5px;
            right: 5px;
            z-index: 5;
            width: 28px;
            height: 28px;
            border-radius: 50%;
            font-size: 14px;
            background-color: rgba(255, 255, 255, 0.8);
            border: 1px solid rgba(0, 0, 0, 0.1);
            color: #333;
            cursor: pointer;
            display: flex;
            align-items: center;
            justify-content: center;
            transition: background-color 0.2s, transform 0.2s;
        }

        .eyedropper-btn:hover {
            background-color: rgba(255, 255, 255, 1);
            transform: scale(1.1);
        }

        .eyedropper-btn.hidden {
            display: none;
        }

        footer {
            height: var(--footer-height);
            text-align: center;
            padding: 20px;
            box-sizing: border-box;
            background-color: #f2f2f2;
            color: #666;
            font-size: 14px;
            flex-shrink: 0;
        }

        .footer-links {
            margin-top: 10px;
        }

        .footer-links a {
            color: var(--primary-color);
            text-decoration: none;
            margin: 0 10px;
        }

        .top-bar a,
        .footer-links a,
        .copy-btn,
        .clear-btn,
        .eyedropper-btn {
            display: inline-flex;
            align-items: center;
            justify-content: center;
            gap: 0.45em;
        }

        .footer-links a:hover {
            text-decoration: underline;
        }

        .tool-description {
            max-width: 800px;
            margin: 20px auto;
            padding: 20px;
            background-color: var(--container-bg);
            border-radius: 8px;
            box-shadow: 0 2px 10px rgba(0, 0, 0, 0.1);
            font-size: 14px;
            line-height: 1.6;
            color: #666;
        }

        .tool-description h3 {
            margin-top: 0;
            margin-bottom: 10px;
            font-size: 1.1em;
            color: #444;
            text-align: left;
        }

        .tool-description p {
            margin: 0 0 10px 0;
        }

        .tool-description p:last-child {
            margin-bottom: 0;
        }

        .tool-description code {
            background-color: #e9e9e9;
            padding: 2px 5px;
            border-radius: 4px;
            font-family: "SF Mono", "Consolas", "Menlo", monospace;
        }

        /* Styles for PC (large screens) */
        @media (min-width: 1024px) {
            .container {
                width: 60vw;
                max-width: none;
                margin: 2vh auto;
                padding: 20px;
            }

            .color-grid {
                grid-template-rows: repeat(12, 1fr);
                gap: 4px;
            }

            .tool-description {
                width: 60vw;
                max-width: none;
                margin: 2vh auto;
            }
        }

        /* Styles for mobile (small screens) */

/* --- Color Selection Indicator --- */
.color-box.selected {
    outline: 2px solid var(--primary-color);
    outline-offset: 1px;
    transform: scale(1.1);
}

/* A centered dot for the selected color box */
.color-box.selected::after {
    content: '';
    position: absolute;
    top: 50%;
    left: 50%;
    transform: translate(-50%, -50%);
    width: 6px;
    height: 6px;
    border-radius: 50%;
    background-color: rgba(255, 255, 255, 0.7);
    box-shadow: 0 0 2px rgba(0, 0, 0, 0.5);
}

/* --- Toast Notification --- */
#toast-notification {
    position: fixed;
    bottom: 20px;
    left: 50%;
    transform: translateX(-50%);
    background-color: #323232;
    color: white;
    padding: 12px 20px;
    border-radius: 8px;
    z-index: 1000;
    opacity: 0;
    visibility: hidden;
    transition: opacity 0.3s ease, visibility 0.3s ease, bottom 0.3s ease;
    font-size: 14px;
}

#toast-notification.show {
    opacity: 1;
    visibility: visible;
    bottom: 30px;
}

/* --- Color History --- */
.history-section {
    max-width: 400px;
    width: 100%;
    margin: 15px auto;
    background-color: #f5f5f5;
    border-radius: 5px;
    padding: 10px;
    box-sizing: border-box;
}

.history-section h4 {
    margin: 0 0 8px 0;
    font-size: 14px;
    font-weight: 600;
    color: #555;
}

.history-container {
    display: flex;
    justify-content: flex-start;
    align-items: center;
    flex-wrap: wrap;
    gap: 8px;
    min-height: 34px; /* Fixed height = 24px box + 2*5px padding */
}

.history-box {
    width: 24px;
    height: 24px;
    border-radius: 5px;
    border: 1px solid rgba(0,0,0,0.1);
    cursor: pointer;
    transition: transform 0.2s ease;
    background-image: linear-gradient(45deg, #ccc 25%, transparent 25%), linear-gradient(-45deg, #ccc 25%, transparent 25%), linear-gradient(45deg, transparent 75%, #ccc 75%), linear-gradient(-45deg, transparent 75%, #ccc 75%);
    background-size: 8px 8px;
    background-position: 0 0, 0 4px, 4px -4px, -4px 0px;
    position: relative;
    overflow: hidden;
}

.history-box::before {
    content: '';
    position: absolute;
    top: 0; right: 0; bottom: 0; left: 0;
    background-color: var(--history-color);
}

.history-box:hover {
    transform: scale(1.15);
    border-color: var(--primary-color);
}

.history-empty-message {
    font-size: 13px;
    color: #888;
}

.history-header {
    display: flex;
    justify-content: space-between;
    align-items: center;
}

.history-header h4 {
    margin-bottom: 0; /* Override default margin */
}

.clear-btn {
    background: none;
    border: none;
    color: #999;
    cursor: pointer;
    font-size: 1rem;
    padding: 4px;
    border-radius: 50%;
    line-height: 1;
    width: 24px;
    height: 24px;
    display: flex;
    align-items: center;
    justify-content: center;
    transition: color 0.2s, background-color 0.2s;
}

.clear-btn:hover {
    color: #333;
    background-color: #e0e0e0;
}

.faq-inline-icon {
    color: inherit;
}

.faq-success-icon {
    color: #28a745;
}

/* --- Pro Mode & Alpha Controls --- */
.pro-mode-switch-container {
    display: flex;
    justify-content: center;
    align-items: center;
    gap: 10px;
    margin-bottom: 15px;
}

.pro-mode-label {
    font-size: 14px;
    color: #666;
    font-weight: 500;
}

.switch {
    position: relative;
    display: inline-block;
    width: 44px;
    height: 24px;
}

.switch input { 
    opacity: 0;
    width: 0;
    height: 0;
}

.slider {
    position: absolute;
    cursor: pointer;
    top: 0;
    left: 0;
    right: 0;
    bottom: 0;
    background-color: #ccc;
    transition: .4s;
}

.slider:before {
    position: absolute;
    content: "";
    height: 18px;
    width: 18px;
    left: 3px;
    bottom: 3px;
    background-color: white;
    transition: .4s;
}

input:checked + .slider {
    background-color: var(--primary-color);
}

input:checked + .slider:before {
    transform: translateX(20px);
}

.slider.round {
    border-radius: 24px;
}

.slider.round:before {
    border-radius: 50%;
}

.alpha-container {
    max-width: 400px;
    width: 100%;
    margin: 5px auto 0;
    display: flex;
    align-items: center;
    gap: 10px;
}

#alpha-slider-track {
    flex-grow: 1;
    height: 25px;
    border: 1px solid var(--border-color);
    border-radius: 3px;
    padding: 0 2px;
    box-sizing: border-box;
    background-image: linear-gradient(45deg, #ccc 25%, transparent 25%), linear-gradient(-45deg, #ccc 25%, transparent 25%), linear-gradient(45deg, transparent 75%, #ccc 75%), linear-gradient(-45deg, transparent 75%, #ccc 75%);
    background-size: 16px 16px;
    background-position: 0 0, 0 8px, 8px -8px, -8px 0px;
}

#alpha-slider {
    width: 100%;
    -webkit-appearance: none;
    appearance: none;
    height: 100%;
    background: transparent;
    cursor: pointer;
    margin: 0;
}

#alpha-value-input {
    font-family: "SF Mono", "Consolas", "Menlo", monospace;
    font-size: 14px;
    color: #555;
    width: 45px;
    text-align: right;
    padding: 2px 4px;
    border: 1px solid #ccc;
    border-radius: 3px;
    background-color: white;
    box-sizing: border-box;
}

#alpha-value-input:focus {
    outline: none;
    border-color: var(--primary-color);
    box-shadow: 0 0 0 2px rgba(0, 123, 255, 0.25);
}

/* Custom Slider Thumb */
#alpha-slider::-webkit-slider-thumb {
    -webkit-appearance: none;
    appearance: none;
    width: 14px;
    height: 22px;
    background: #fff;
    border: 1px solid #888;
    border-radius: 3px;
    box-shadow: 0 0 2px rgba(0,0,0,0.3);
}

#alpha-slider::-moz-range-thumb {
    width: 14px;
    height: 22px;
    background: #fff;
    border: 1px solid #888;
    border-radius: 3px;
    box-shadow: 0 0 2px rgba(0,0,0,0.3);
}

/* --- Contrast Checker, Format Toggle, and Keyboard Focus --- */

.alpha-value-container {
    display: flex;
    align-items: center;
    gap: 5px;
}

.alpha-format-toggle {
    background: none;
    border: 1px solid #ccc;
    border-radius: 3px;
    padding: 2px 6px;
    font-size: 12px;
    cursor: pointer;
    color: #666;
    height: 28px; /* Match input height */
    line-height: 1;
}

.alpha-format-toggle:hover {
    background-color: #f0f0f0;
}

#alpha-slider-track:focus-within {
    border-color: var(--primary-hover);
    box-shadow: 0 0 2px var(--primary-color);
}

#alpha-slider:focus {
    outline: 3px solid var(--primary-color);
    outline-offset: 2px;
}

.contrast-checker {
    max-width: 400px;
    width: 100%;
    margin: 15px auto 0;
    background-color: #f8f9fa;
    border: 1px solid var(--border-color);
    border-radius: 5px;
    padding: 12px;
    box-sizing: border-box;
}

.contrast-checker h4 {
    margin: 0 0 10px 0;
    font-size: 14px;
    font-weight: 600;
    color: #444;
}

.contrast-samples {
    display: flex;
    gap: 10px;
    justify-content: space-between;
}

.contrast-sample {
    flex: 1;
    min-width: 0;
}

.sample-preview {
    height: 40px;
    border-radius: 3px;
    display: flex;
    align-items: center;
    justify-content: center;
    margin-bottom: 5px;
    border: 1px solid var(--border-color);
}

.sample-text {
    font-size: 16px;
    font-weight: bold;
}

.sample-info {
    display: flex;
    flex-direction: column;
    align-items: center;
    font-size: 12px;
}

.bg-label {
    color: #666;
    margin-bottom: 2px;
}

.contrast-ratio {
    font-family: "SF Mono", "Consolas", "Menlo", monospace;
    font-size: 11px;
    color: #555;
}

.contrast-rating {
    font-size: 11px;
    font-weight: bold;
    margin-top: 2px;
}

.rating-aa {
    color: #28a745;
}

.rating-aaa {
    color: #20c997;
}

.rating-fail {
    color: #dc3545;
}

.sample-info .custom-bg-input {
    border: 1px solid #ccc;
    border-radius: 3px;
    width: 24px;
    height: 24px;
    padding: 0;
    cursor: pointer;
    background-color: transparent;
    margin: 0 auto; /* Center the input */
}

.sample-info .custom-bg-input::-webkit-color-swatch-wrapper {
    padding: 0;
}

.sample-info .custom-bg-input::-webkit-color-swatch {
    border: none;
    border-radius: 2px;
}

/* --- Mobile and Tablet Layout Optimizations --- */

/* Tablet (600px - 1023px) */
@media (min-width: 600px) and (max-width: 1023px) {
    .controls {
        gap: 12px; /* Tighter gap for tablets */
    }
}

/* Tablet and Mobile (<= 1023px) */
@media (max-width: 1023px) {
    html,
    body {
        height: auto;
        overflow: auto;
    }

    .color-grid {
        height: auto; /* Remove fixed vh height */
        aspect-ratio: 20 / 12;
    }

    /* Fallback for browsers that don't support aspect-ratio */
    @supports not (aspect-ratio: 1) {
        .color-grid {
            position: relative;
            height: 0;
            padding-top: 60%; /* 12 / 20 = 0.6 */
        }
        .color-grid > * {
            position: absolute;
            top: 0; left: 0; right: 0; bottom: 0;
        }
    }

    .copy-btn,
    .clear-btn,
    .alpha-format-toggle {
        /* Ensure buttons are easy to tap */
        min-width: 44px;
        min-height: 44px;
        display: flex;
        align-items: center;
        justify-content: center;
    }
}

/* Mobile-only (<= 599px) */
@media (max-width: 599px) {
    .controls {
        flex-direction: column;
        gap: 20px;
        margin-bottom: 80px; /* Avoid virtual keyboard overlap */
    }

    .color-values input {
        height: 40px;
        font-size: 16px; /* Avoid iOS auto-zoom on focus */
    }

    .contrast-samples {
        flex-direction: column;
        gap: 8px;
    }
}