:root {
    --primary-color: #4A90E2;
    --primary-hover: #357ABD;
    --success-color: #50E3C2;
    --error-color: #D0021B;
    --light-grey: #f7f8fa;
    --medium-grey: #e4e8f0;
    --dark-grey: #6b778d;
    --text-color: #172b4d;
    --bg-color: #f0f4f8;
    --white: #ffffff;
    --border-radius: 12px;
    --box-shadow: 0 10px 30px rgba(0, 0, 0, 0.07);
}

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

body {
    font-family: 'Poppins', sans-serif;
    background-color: var(--bg-color);
    color: var(--text-color);
    display: flex;
    justify-content: center;
    align-items: flex-start;
    min-height: 100vh;
    padding: 30px;
}

.converter-app {
    width: 100%;
    max-width: 800px;
}

.app-header {
    text-align: center;
    margin-bottom: 30px;
}
.app-icon {
    width: 64px;
    height: 64px;
    margin-bottom: 1rem;
    object-fit: contain;
}
.app-header h1 {
    font-size: 2.25rem;
    font-weight: 700;
    color: var(--text-color);
    margin-bottom: 8px;
}
.app-header p {
    font-size: 1rem;
    color: var(--dark-grey);
    max-width: 550px;
    margin: 0 auto;
}

.upload-container {
    background: var(--white);
    border-radius: var(--border-radius);
    box-shadow: var(--box-shadow);
    padding: 30px;
}

.drop-zone {
    border: 2px dashed var(--medium-grey);
    border-radius: var(--border-radius);
    padding: 40px;
    text-align: center;
    cursor: pointer;
    transition: background-color 0.3s, border-color 0.3s;
}
.drop-zone.drag-over {
    background-color: var(--light-grey);
    border-color: var(--primary-color);
}
.drop-zone-content .upload-icon {
    width: 60px;
    height: 60px;
    object-fit: contain;
    margin-bottom: 15px;
}
.drop-zone-content h3 { font-size: 1.2rem; margin-bottom: 5px; }
.drop-zone-content p { color: var(--dark-grey); margin-bottom: 15px; }
#file-input { display: none; }
.browse-btn {
    background-color: var(--primary-color);
    color: var(--white);
    padding: 10px 20px;
    border-radius: 8px;
    font-weight: 500;
    transition: background-color 0.3s;
}
.browse-btn:hover { background-color: var(--primary-hover); }

.supported-formats {
    margin-top: 15px;
    font-size: 0.8rem;
    color: #a0aec0;
    font-weight: 500;
}

.preview-container { margin-top: 20px; }
.file-preview-item {
    display: flex;
    align-items: center;
    background: var(--light-grey);
    border-radius: 8px;
    padding: 15px;
    margin-bottom: 10px;
    animation: fadeIn 0.5s ease;
    gap: 15px;
}

.thumbnail {
    width: 50px;
    height: 50px;
    border-radius: 6px;
    object-fit: cover;
    flex-shrink: 0;
}

.file-details {
    flex-grow: 1;
    min-width: 0;
}

.file-name {
    font-weight: 600;
    font-size: 0.9rem;
    white-space: nowrap;
    overflow: hidden;
    text-overflow: ellipsis;
}
.file-size { font-size: 0.8rem; color: var(--dark-grey); }

.status-indicator, .action-area {
    width: auto;
    height: 30px;
    display: flex;
    justify-content: center;
    align-items: center;
    flex-shrink: 0;
}

.action-area {
    min-width: 100px;
    justify-content: flex-end;
}

.spinner {
    width: 24px;
    height: 24px;
    border: 3px solid var(--medium-grey);
    border-top-color: var(--primary-color);
    border-radius: 50%;
    animation: spin 1s linear infinite;
}
@keyframes spin { 0% { transform: rotate(0deg); } 100% { transform: rotate(360deg); } }
.status-icon { width: 24px; height: 24px; }
.success { color: var(--success-color); }
.error { color: var(--error-color); }

.action-buttons {
    display: none;
    grid-template-columns: 1fr 1fr 1fr;
    gap: 15px;
    margin-top: 30px;
}
.action-btn {
    border: none;
    padding: 12px;
    border-radius: 8px;
    font-weight: 600;
    cursor: pointer;
    transition: all 0.3s;
    display: flex;
    justify-content: center;
    align-items: center;
    gap: 8px;
}
.action-btn:hover { transform: translateY(-2px); box-shadow: 0 4px 10px rgba(0,0,0,0.1); }
.action-btn svg { transition: transform 0.2s; }
.action-btn:hover svg { transform: scale(1.1); }
.action-btn.convert { background: var(--primary-color); color: var(--white); }
.action-btn.download-zip { background: var(--success-color); color: var(--white); display: none; }
.action-btn.clear { background: var(--medium-grey); color: var(--dark-grey); }

.download-link {
    display: inline-flex;
    align-items: center;
    gap: 5px;
    background: var(--success-color);
    color: var(--white);
    padding: 5px 10px;
    border-radius: 5px;
    text-decoration: none;
    font-size: 0.8rem;
    font-weight: 500;
}
.download-link svg { width: 16px; height: 16px; }

@media (max-width: 600px) {
    body { padding: 15px; }
    .upload-container { padding: 20px; }
    .action-buttons { grid-template-columns: 1fr; }
}