:root {
    /* Color Palette */
    --bg-color: #f4f4f4;
    --text-color: #333;
    --header-bg: #333;
    --header-text: #fff;
    --accent-color: #007bff;
    --accent-hover: #0056b3;
    --border-color: #ccc;
    
    /* UI Components */
    --modal-overlay-bg: rgba(0,0,0,0.6);
    --modal-content-bg: #fff;
    --drop-area-bg: #fafafa;
    --drop-area-hover: #e9e9e9;
    --button-bg: #4a4a4a;
    --button-hover-bg: #666;
    --error-bg: #d9534f;
    --error-text: #fff;
}

body {
    font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, 'Helvetica Neue', Arial, sans-serif;
    margin: 0;
    background-color: var(--bg-color);
    color: var(--text-color);
    line-height: 1.6;
}

/* Header */
header {
    background-color: var(--header-bg);
    color: var(--header-text);
    padding: 10px 20px;
    display: flex;
    justify-content: space-between;
    align-items: center;
}

header h1 {
    margin: 0;
    font-size: 1.5rem;
}

/* Utilities */
.hidden {
    display: none !important;
}

/* Modal */
.modal-overlay {
    position: fixed;
    z-index: 1000;
    left: 0;
    top: 0;
    width: 100%;
    height: 100%;
    background-color: var(--modal-overlay-bg);
    display: flex;
    justify-content: center;
    align-items: center;
}

.modal-content {
    background-color: var(--modal-content-bg);
    padding: 20px;
    border-radius: 8px;
    width: 90%;
    max-width: 800px;
    max-height: 90vh;
    display: flex;
    flex-direction: column;
    box-shadow: 0 4px 15px rgba(0,0,0,0.2);
}

.modal-header {
    padding-bottom: 10px;
    border-bottom: 1px solid var(--border-color);
    display: flex;
    justify-content: space-between;
    align-items: center;
}

.modal-body {
    padding: 15px 0;
    overflow-y: auto;
}

.modal-footer {
    text-align: right;
    padding-top: 15px;
    border-top: 1px solid var(--border-color);
}

.modal-close-button {
    cursor: pointer;
    font-size: 1.5rem;
    font-weight: bold;
    color: #999;
}
.modal-close-button:hover {
    color: #333;
}

/* Drop Area */
.drop-area {
    border: 2px dashed var(--border-color);
    border-radius: 8px;
    padding: 2rem;
    text-align: center;
    background-color: var(--drop-area-bg);
    cursor: pointer;
    transition: background-color 0.2s ease;
    position: relative;
    margin-bottom: 1rem;
}
.drop-area:hover, .drop-area.dragover {
    background-color: var(--drop-area-hover);
}

/* Buttons */
button {
    padding: 8px 16px;
    border: none;
    border-radius: 4px;
    cursor: pointer;
    transition: background-color 0.2s;
    font-size: 1rem;
}
button:disabled {
    opacity: 0.6;
    cursor: not-allowed;
}

/* Error Message */
.error-message {
    position: fixed;
    bottom: 20px;
    left: 50%;
    transform: translateX(-50%);
    background-color: var(--error-bg);
    color: var(--error-text);
    padding: 10px 20px;
    border-radius: 5px;
    box-shadow: 0 2px 10px rgba(0,0,0,0.2);
    z-index: 2000;
}