:root {
    --primary-color: #1a5276;
    --primary-hover: #154360;
    --secondary-color: #2471a3;
    --accent-color: #3498db;
    --danger-color: #ef476f;
    --success-color: #06d6a0;
    --warning-color: #ffd166;
    --dark-color: #2b2d42;
    --light-color: #f8f9fa;
    --grey-color: #e9ecef;
    --text-color: #2b2d42;
    --text-muted: #6c757d;
    --border-radius: 12px;
    --box-shadow: 0 8px 30px rgba(0, 0, 0, 0.12);
    --transition: all 0.3s ease;
}

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

body {
    font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
    line-height: 1.6;
    color: var(--text-color);
    background: linear-gradient(135deg, #f5f7fa 0%, #c3cfe2 100%);
    min-height: 100vh;
    padding: 40px 20px;
}

.container {
    max-width: 900px;
    margin: 0 auto;
    background-color: #fff;
    border-radius: var(--border-radius);
    box-shadow: var(--box-shadow);
    overflow: hidden;
    position: relative;
}

.app-header {
    background: linear-gradient(90deg, var(--primary-color), var(--secondary-color));
    color: white;
    padding: 30px;
    text-align: center;
    border-radius: var(--border-radius) var(--border-radius) 0 0;
    position: relative;
}

.app-title {
    font-size: 2.2rem;
    margin-bottom: 10px;
    font-weight: 700;
}

.app-subtitle {
    font-size: 1.1rem;
    opacity: 0.85;
    font-weight: 400;
}

.app-body {
    padding: 30px;
}

.intro-box {
    background-color: rgba(26, 82, 118, 0.1);
    border-radius: var(--border-radius);
    padding: 20px;
    margin-bottom: 25px;
    border-left: 4px solid var(--primary-color);
}

.intro-title {
    font-weight: 600;
    color: var(--primary-color);
    font-size: 1.1rem;
    margin-bottom: 10px;
    display: flex;
    align-items: center;
}

.intro-title i {
    margin-right: 8px;
}

.intro-text {
    color: var(--text-color);
    font-size: 0.95rem;
    margin-bottom: 10px;
}

.intro-bullets {
    list-style-type: none;
    margin-left: 10px;
    margin-top: 10px;
}

.intro-bullets li {
    position: relative;
    padding-left: 20px;
    margin-bottom: 8px;
    font-size: 0.9rem;
}

.intro-bullets li:before {
    content: "✓";
    position: absolute;
    left: 0;
    color: var(--primary-color);
    font-weight: bold;
}

.dropzone {
    border: 3px dashed var(--grey-color);
    border-radius: var(--border-radius);
    padding: 40px 30px;
    text-align: center;
    margin-bottom: 30px;
    cursor: pointer;
    transition: var(--transition);
    background-color: var(--light-color);
}

.dropzone:hover {
    border-color: var(--primary-color);
    background-color: rgba(26, 82, 118, 0.05);
}

.dropzone-active {
    border-color: var(--success-color) !important;
    background-color: rgba(6, 214, 160, 0.1) !important;
}

.dropzone-icon {
    font-size: 3rem;
    color: var(--primary-color);
    margin-bottom: 15px;
}

.dropzone-text {
    font-size: 1.2rem;
    margin-bottom: 10px;
    color: var(--text-color);
}

.dropzone-subtext {
    color: var(--text-muted);
    font-size: 0.95rem;
}

.file-list {
    margin-bottom: 25px;
}

.file-item {
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding: 15px;
    background-color: var(--light-color);
    border-radius: var(--border-radius);
    margin-bottom: 10px;
    border-left: 4px solid var(--primary-color);
    transition: var(--transition);
}

.file-item:hover {
    transform: translateY(-2px);
    box-shadow: 0 4px 12px rgba(0, 0, 0, 0.08);
}

.file-details {
    flex: 1;
}

.file-name {
    font-weight: 600;
    margin-bottom: 4px;
    color: var(--dark-color);
    display: flex;
    align-items: center;
}

.file-name i {
    color: var(--danger-color);
    margin-right: 8px;
}

.file-meta {
    display: flex;
    gap: 15px;
    color: var(--text-muted);
    font-size: 0.9rem;
}

.file-meta span {
    display: flex;
    align-items: center;
}

.file-meta i {
    margin-right: 5px;
    font-size: 0.8rem;
}

.btn {
    display: inline-block;
    font-weight: 600;
    color: white;
    text-align: center;
    vertical-align: middle;
    cursor: pointer;
    padding: 12px 24px;
    font-size: 1rem;
    line-height: 1.5;
    border-radius: var(--border-radius);
    transition: var(--transition);
    border: none;
    outline: none;
    box-shadow: 0 4px 6px rgba(50, 50, 93, 0.11), 0 1px 3px rgba(0, 0, 0, 0.08);
}

.btn-primary {
    background-color: var(--primary-color);
}

.btn-primary:hover {
    background-color: var(--primary-hover);
    transform: translateY(-1px);
}

.btn-primary:disabled {
    background-color: var(--grey-color);
    cursor: not-allowed;
    color: var(--text-muted);
    box-shadow: none;
}

.btn-secondary {
    background-color: var(--text-muted);
}

.btn-secondary:hover {
    background-color: #5a6268;
    transform: translateY(-1px);
}

.btn-download {
    background-color: var(--success-color);
    padding: 8px 16px;
    font-size: 0.9rem;
}

.btn-download:hover {
    background-color: #05b589;
}

.btn-block {
    display: block;
    width: 100%;
}

.section-title {
    font-size: 1.6rem;
    font-weight: 600;
    margin-bottom: 20px;
    color: var(--dark-color);
    position: relative;
    padding-bottom: 10px;
}

.section-title:after {
    content: '';
    position: absolute;
    bottom: 0;
    left: 0;
    width: 60px;
    height: 4px;
    background: var(--primary-color);
    border-radius: 2px;
}

.loading {
    text-align: center;
    padding: 30px;
    display: none;
}

.spinner {
    display: inline-block;
    width: 50px;
    height: 50px;
    border: 4px solid rgba(26, 82, 118, 0.2);
    border-radius: 50%;
    border-top-color: var(--primary-color);
    animation: spin 1s ease-in-out infinite;
    margin-bottom: 15px;
}

@keyframes spin {
    to { transform: rotate(360deg); }
}

.loading-text {
    font-size: 1.1rem;
    color: var(--primary-color);
    font-weight: 500;
}

.result-container {
    margin-top: 30px;
    border-top: 2px solid var(--grey-color);
    padding-top: 30px;
    display: none;
}

.alert {
    padding: 16px;
    margin-bottom: 20px;
    border-radius: var(--border-radius);
    font-weight: 500;
}

.alert-info {
    background-color: rgba(52, 152, 219, 0.15);
    color: #2980b9;
    border-left: 4px solid #2980b9;
}

.alert-success {
    background-color: rgba(6, 214, 160, 0.15);
    color: #06d6a0;
    border-left: 4px solid #06d6a0;
}

.alert-warning {
    background-color: rgba(255, 209, 102, 0.15);
    color: #e09f3e;
    border-left: 4px solid #e09f3e;
}

.alert-danger {
    background-color: rgba(239, 71, 111, 0.15);
    color: #d90429;
    border-left: 4px solid #d90429;
}

.alert i {
    margin-right: 8px;
}

.page-count-summary {
    background-color: var(--light-color);
    padding: 15px;
    border-radius: var(--border-radius);
    margin-bottom: 20px;
    border-left: 4px solid var(--accent-color);
}

.page-count-item {
    display: flex;
    justify-content: space-between;
    padding: 8px 0;
    border-bottom: 1px solid var(--grey-color);
}

.page-count-item:last-child {
    border-bottom: none;
    font-weight: 600;
}

.new-merge-btn-container {
    text-align: center;
    margin-top: 30px;
}

.app-footer {
    text-align: center;
    padding: 20px;
    background-color: var(--grey-color);
    color: var(--text-muted);
    font-size: 0.9rem;
    border-top: 1px solid #dee2e6;
    border-radius: 0 0 var(--border-radius) var(--border-radius);
}

.designer-signature {
    font-weight: 600;
    color: var(--dark-color);
}

.wcl-branding {
    display: inline-block;
    margin-left: 5px;
    font-weight: 600;
    color: var(--primary-color);
}

/* Responsive adjustments */
@media (max-width: 768px) {
    .app-title {
        font-size: 1.8rem;
    }
    
    .app-body {
        padding: 20px;
    }
    
    .dropzone {
        padding: 30px 20px;
    }
    
    .btn {
        padding: 10px 20px;
    }

    .file-meta {
        flex-direction: column;
        gap: 5px;
    }
}