:root {
    --primary-color: #007bff;
    --primary-hover-color: #0056b3;
    --secondary-color: #6c757d;
    --secondary-hover-color: #545b62;
    --danger-color: #dc3545;
    --danger-hover-color: #c82333;
    --light-color: #f8f9fa;
    --dark-color: #343a40;
    --text-color: #212529;
    --border-color: #dee2e6;
    --background-color: #e9ecef; /* Lighter background for the page */
    --surface-color: #ffffff; /* For cards, modals, etc. */
    --font-family-sans-serif: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, "Helvetica Neue", Arial, sans-serif;
    --border-radius: 0.3rem;
    --box-shadow: 0 0.125rem 0.25rem rgba(0, 0, 0, 0.075);
    --input-focus-border-color: #80bdff;
    --input-focus-box-shadow: 0 0 0 0.2rem rgba(0, 123, 255, 0.25);
}

body {
    font-family: var(--font-family-sans-serif);
    margin: 0;
    background-color: var(--background-color);
    color: var(--text-color);
    display: flex;
    flex-direction: column;
    min-height: 100vh;
    line-height: 1.6;
}

header {
    background-color: var(--dark-color);
    color: var(--light-color);
    padding: 1.5rem 1rem;
    text-align: center;
    box-shadow: 0 2px 4px rgba(0,0,0,0.1);
}

header h1 {
    margin: 0;
    font-size: 1.75rem;
    font-weight: 500;
}

main {
    flex: 1;
    padding: 1.5rem;
    display: grid;
    grid-template-columns: 350px 1fr; /* Wider controls panel */
    gap: 1.5rem;
    max-width: 1400px; /* Wider max-width */
    margin: 0 auto;
    width: 100%;
    box-sizing: border-box;
}

#controls,
#mosaic-display-area,
#pasted-images-preview {
    background-color: var(--surface-color);
    padding: 1.5rem;
    border-radius: var(--border-radius);
    box-shadow: var(--box-shadow);
}

h2 {
    font-size: 1.25rem;
    color: var(--dark-color);
    margin-top: 0;
    margin-bottom: 1rem;
    border-bottom: 1px solid var(--border-color);
    padding-bottom: 0.5rem;
}

.control-group {
    margin-bottom: 1.25rem;
}
.paste-instruction {
    font-size: 0.9rem;
    color: var(--secondary-color);
    text-align: center;
    margin-bottom: 1rem;
    padding: 0.5rem;
    background-color: var(--light-color);
    border: 1px dashed var(--border-color);
    border-radius: var(--border-radius);
}

.control-group label {
    display: block;
    margin-bottom: 0.5rem;
    font-weight: 500;
    color: #495057;
}

.control-group input[type="number"],
#paste-area {
    width: 100%;
    padding: 0.65rem 0.75rem; /* Increased padding */
    box-sizing: border-box;
    border: 1px solid var(--border-color);
    border-radius: var(--border-radius);
    font-size: 0.9rem;
    transition: border-color 0.15s ease-in-out, box-shadow 0.15s ease-in-out;
}

.control-group input[type="number"]:focus,
#paste-area:focus {
    border-color: var(--input-focus-border-color);
    outline: 0;
    box-shadow: var(--input-focus-box-shadow);
}

#paste-area {
    min-height: 120px; /* Increased height */
    background-color: var(--light-color);
    overflow-y: auto;
    resize: vertical;
}

#paste-area[aria-placeholder]:empty::before {
    content: attr(aria-placeholder);
    color: #6c757d;
    font-style: italic;
}

.action-buttons {
    display: flex;
    flex-direction: column; /* Stack buttons vertically */
    gap: 0.75rem; /* Space between buttons */
}

button {
    padding: 0.65rem 1rem; /* Consistent padding */
    font-size: 0.9rem;
    font-weight: 500;
    border-radius: var(--border-radius);
    border: 1px solid transparent;
    cursor: pointer;
    transition: background-color 0.15s ease-in-out, border-color 0.15s ease-in-out, color 0.15s ease-in-out;
    width: 100%; /* Make buttons full width of their container */
    box-sizing: border-box;
}

.button-primary {
    background-color: var(--primary-color);
    color: white;
    border-color: var(--primary-color);
}

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

.button-secondary {
    background-color: var(--secondary-color);
    color: white;
    border-color: var(--secondary-color);
}

.button-secondary:hover {
    background-color: var(--secondary-hover-color);
    border-color: var(--secondary-hover-color);
}

.button-danger {
    background-color: var(--danger-color);
    color: white;
    border-color: var(--danger-color);
}

.button-danger:hover {
    background-color: var(--danger-hover-color);
    border-color: var(--danger-hover-color);
}


#mosaic-canvas {
    border: 1px solid var(--border-color);
    display: block;
    max-width: 100%;
    height: auto;
    background-color: #f8f9fa; /* Light background for canvas */
    border-radius: var(--border-radius);
}

#image-previews {
    display: flex;
    flex-wrap: wrap;
    gap: 10px;
    margin-top: 10px;
    border: 1px solid var(--border-color);
    padding: 10px;
    min-height: 60px; /* Slightly increased min-height */
    background-color: var(--light-color);
    border-radius: var(--border-radius);
}

#image-previews img {
    max-width: 70px; /* Slightly smaller for better fit */
    max-height: 70px;
    border: 1px solid #ced4da;
    object-fit: cover;
    border-radius: calc(var(--border-radius) * 0.8); /* Slightly smaller radius */
    box-shadow: 0 1px 2px rgba(0,0,0,0.05);
}

footer {
    background-color: var(--dark-color);
    color: var(--light-color);
    text-align: center;
    padding: 1rem;
    margin-top: auto; /* Pushes footer to bottom */
    font-size: 0.9rem;
}

/* Responsive adjustments */
@media (max-width: 992px) { /* Adjusted breakpoint for better layout shift */
    main {
        grid-template-columns: 1fr; /* Stack sections on smaller screens */
    }

    #controls,
    #mosaic-display-area,
    #pasted-images-preview {
        margin-bottom: 1.5rem;
    }

    .action-buttons {
        flex-direction: row; /* Buttons side-by-side on smaller screens if space allows */
        flex-wrap: wrap; /* Allow wrapping if not enough space */
    }

    .action-buttons button {
        flex-grow: 1; /* Allow buttons to grow and share space */
    }
}

@media (max-width: 576px) {
    header h1 {
        font-size: 1.5rem;
    }
    main {
        padding: 1rem;
        gap: 1rem;
    }
    #controls,
    #mosaic-display-area,
    #pasted-images-preview {
        padding: 1rem;
    }
    .action-buttons {
        flex-direction: column; /* Stack buttons again on very small screens */
    }
    button {
        font-size: 0.85rem;
        padding: 0.6rem 0.8rem;
    }
    .control-group input[type="number"],
    #paste-area {
        padding: 0.6rem 0.7rem;
        font-size: 0.85rem;
    }
    #image-previews img {
        max-width: 60px;
        max-height: 60px;
    }
}
/* Modal Styles */
.modal {
    display: none; /* Hidden by default */
    position: fixed; /* Stay in place */
    z-index: 1000; /* Sit on top */
    left: 0;
    top: 0;
    width: 100%;
    height: 100%;
    overflow: auto; /* Enable scroll if needed */
    background-color: rgba(0,0,0,0.6); /* Black w/ opacity */
}

.modal.hidden {
    display: none;
}

.modal:not(.hidden) {
    display: flex; /* Use flexbox to center content */
    align-items: center;
    justify-content: center;
}

.modal-content {
    background-color: var(--surface-color);
    margin: auto;
    padding: 25px;
    border: 1px solid var(--border-color);
    width: 80%;
    max-width: 600px;
    border-radius: var(--border-radius);
    box-shadow: 0 5px 15px rgba(0,0,0,0.3);
    position: relative;
    animation: fadeInModal 0.3s ease-out;
}

@keyframes fadeInModal {
    from { opacity: 0; transform: translateY(-20px); }
    to { opacity: 1; transform: translateY(0); }
}

.close-button {
    color: #aaa;
    float: right;
    font-size: 28px;
    font-weight: bold;
    position: absolute;
    top: 10px;
    right: 20px;
}

.close-button:hover,
.close-button:focus {
    color: var(--dark-color);
    text-decoration: none;
    cursor: pointer;
}

.modal-content h2 {
    margin-top: 0;
    color: var(--primary-color);
}

.modal-content p {
    margin-bottom: 1rem;
    line-height: 1.6;
}

.modal-content ul {
    list-style-type: disc;
    margin-left: 20px;
    margin-bottom: 1.5rem;
}

.modal-content ul li {
    margin-bottom: 0.5rem;
}

.modal-content .button-primary {
    display: block;
    width: auto; /* Don't make it full width */
    margin: 1rem auto 0; /* Center the button */
    padding: 0.75rem 1.5rem;
}