:root {
    --bg-color: #f8f9fa;
    --card-bg: #ffffff;
    --text-main: #212529;
    --text-muted: #6c757d;
    --accent-color: #007bff;
    --accent-gradient: linear-gradient(135deg, #007bff, #00d4ff);
    --border-color: #dee2e6;
    --drop-zone-bg: #f1f3f5;
    --toggle-bg: #e9ecef;
    --shadow: 0 4px 6px rgba(0, 0, 0, 0.05), 0 1px 3px rgba(0, 0, 0, 0.1);
    --header-height: 70px;
}

body.dark-mode {
    --bg-color: #1a1a1a;
    --card-bg: #2d2d2d;
    --text-main: #f8f9fa;
    --text-muted: #adb5bd;
    --accent-color: #339af0;
    --border-color: #404040;
    --drop-zone-bg: #383838;
    --toggle-bg: #404040;
    --shadow: 0 10px 30px rgba(0, 0, 0, 0.5);
}

* {
    box-sizing: border-box;
    margin: 0;
    padding: 0;
}

body {
    font-family: 'Pretendard', -apple-system, BlinkMacSystemFont, system-ui, Roboto, sans-serif;
    background-color: var(--bg-color);
    color: var(--text-main);
    line-height: 1.6;
    transition: background-color 0.3s ease, color 0.3s ease;
}

.app-container {
    max-width: 1200px;
    margin: 0 auto;
    min-height: 100vh;
    display: flex;
    flex-direction: column;
}

header {
    height: var(--header-height);
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding: 0 2rem;
    background-color: var(--card-bg);
    box-shadow: var(--shadow);
    position: sticky;
    top: 0;
    z-index: 100;
}

.logo {
    font-size: 1.5rem;
    font-weight: 800;
    color: var(--accent-color);
}

.logo span {
    color: var(--text-main);
}

#dark-mode-toggle {
    background-color: var(--toggle-bg);
    border: none;
    border-radius: 50%;
    width: 40px;
    height: 40px;
    cursor: pointer;
    font-size: 1.2rem;
    display: flex;
    justify-content: center;
    align-items: center;
    transition: transform 0.2s ease;
}

#dark-mode-toggle:hover {
    transform: scale(1.1);
}

main {
    flex: 1;
    padding: 2rem;
}

.hero {
    text-align: center;
    margin-bottom: 3rem;
}

.hero h1 {
    font-size: 2.5rem;
    margin-bottom: 0.5rem;
    background: var(--accent-gradient);
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
}

.hero p {
    color: var(--text-muted);
    font-size: 1.1rem;
}

.upload-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(350px, 1fr));
    gap: 2rem;
    margin-bottom: 3rem;
}

.upload-card {
    background-color: var(--card-bg);
    border-radius: 20px;
    padding: 2rem;
    box-shadow: var(--shadow);
    transition: transform 0.3s ease;
}

.upload-card:hover {
    transform: translateY(-5px);
}

.upload-card h2 {
    margin-bottom: 1.5rem;
    font-size: 1.25rem;
}

.drop-zone {
    border: 2px dashed var(--border-color);
    border-radius: 15px;
    background-color: var(--drop-zone-bg);
    padding: 2rem;
    text-align: center;
    cursor: pointer;
    position: relative;
    min-height: 250px;
    display: flex;
    flex-direction: column;
    justify-content: center;
    align-items: center;
    transition: border-color 0.3s ease, background-color 0.3s ease;
}

.drop-zone:hover {
    border-color: var(--accent-color);
    background-color: rgba(0, 123, 255, 0.05);
}

.drop-zone-content .icon {
    font-size: 3rem;
    margin-bottom: 1rem;
    display: block;
}

.drop-zone-content p {
    color: var(--text-muted);
    font-size: 0.9rem;
}

.preview-container {
    position: absolute;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    border-radius: 13px;
    overflow: hidden;
    display: none;
}

.preview-container img {
    width: 100%;
    height: 100%;
    object-fit: contain;
    background-color: #000;
}

.preview-container.active {
    display: block;
}

.action-section {
    text-align: center;
}

.primary-btn {
    background: var(--accent-gradient);
    color: white;
    border: none;
    padding: 1rem 3rem;
    font-size: 1.2rem;
    font-weight: 700;
    border-radius: 50px;
    cursor: pointer;
    transition: transform 0.2s ease, box-shadow 0.2s ease, opacity 0.2s ease;
    box-shadow: 0 4px 15px rgba(0, 123, 255, 0.3);
}

.primary-btn:hover:not(:disabled) {
    transform: translateY(-2px);
    box-shadow: 0 6px 20px rgba(0, 123, 255, 0.4);
}

.primary-btn:disabled {
    opacity: 0.5;
    cursor: not-allowed;
    box-shadow: none;
}

footer {
    padding: 2rem;
    text-align: center;
    color: var(--text-muted);
    font-size: 0.9rem;
    border-top: 1px solid var(--border-color);
}

@media (max-width: 600px) {
    .hero h1 {
        font-size: 1.8rem;
    }
    
    .upload-grid {
        grid-template-columns: 1fr;
    }
    
    header {
        padding: 0 1rem;
    }
}