.tool-container {
    --kcover-primary: #0ea5e9;
    --kcover-primary-hover: #0284c7;
    --kcover-secondary: #0369a1;
    --kcover-text: #e2e8f0;
    --kcover-muted: #94a3b8;
    --kcover-border: #334155;
    --kcover-surface: #0f172a;
    --kcover-surface-alt: #111827;
    --kcover-accent-bg: rgba(14, 165, 233, 0.16);
    --kcover-shadow: 0 10px 24px rgba(2, 6, 23, 0.3);
    --primary: var(--kcover-primary);
    --primary-hover: var(--kcover-primary-hover);
    --secondary: var(--kcover-secondary);
    --cover-accent: var(--kcover-primary);
    --text-main: var(--kcover-text);
    --text-muted: var(--kcover-muted);
    --border: var(--kcover-border);
    max-width: 1000px;
    margin: 40px auto;
    padding: 0 20px 110px;
}

body.light-mode .tool-container {
    --kcover-text: #1e293b;
    --kcover-muted: #64748b;
    --kcover-border: #dbe3ef;
    --kcover-surface: #ffffff;
    --kcover-surface-alt: #f8fafc;
    --kcover-accent-bg: rgba(14, 165, 233, 0.08);
    --kcover-shadow: 0 8px 22px rgba(15, 23, 42, 0.08);
}

.tool-header-custom {
    text-align: center;
    margin-bottom: 40px;
}

.tool-header-custom h1 {
    font-size: 2rem;
    font-weight: 800;
    margin-bottom: 10px;
    color: var(--kcover-text);
}

.tool-header-custom p {
    color: var(--kcover-muted);
}

.assembly-stage {
    display: flex;
    justify-content: center;
    align-items: center;
    gap: 40px;
    padding: 40px 0;
    flex-wrap: wrap;
    min-height: 400px;
}

.cover-slot {
    width: 280px;
    aspect-ratio: 1 / 1.414;
    background: var(--kcover-surface);
    border: 3px dashed var(--kcover-border);
    border-radius: 12px;
    position: relative;
    cursor: pointer;
    transition: all 0.25s ease;
    display: flex;
    flex-direction: column;
    align-items: center;
    justify-content: center;
    box-shadow: var(--kcover-shadow);
}

.cover-slot:hover {
    border-color: var(--kcover-primary);
    transform: translateY(-4px);
    box-shadow: 0 20px 34px rgba(14, 165, 233, 0.2);
}

.cover-slot.dragover {
    border-color: var(--kcover-primary);
    background: var(--kcover-accent-bg);
}

.slot-badge {
    position: absolute;
    top: -12px;
    left: 50%;
    transform: translateX(-50%);
    background: var(--kcover-primary);
    color: #fff;
    padding: 4px 12px;
    border-radius: 20px;
    font-size: 0.75rem;
    font-weight: 700;
    text-transform: uppercase;
    box-shadow: 0 4px 10px rgba(2, 6, 23, 0.25);
    z-index: 5;
    white-space: nowrap;
}

.empty-state {
    text-align: center;
    color: var(--kcover-muted);
    padding: 20px;
    pointer-events: none;
}

.empty-state i {
    font-size: 3rem;
    margin-bottom: 15px;
    color: #7b8da8;
    display: block;
}

.empty-state h3 {
    font-size: 1.1rem;
    margin: 0 0 5px;
    color: var(--kcover-text);
}

.empty-state p {
    font-size: 0.9rem;
    margin: 0;
    color: var(--kcover-muted);
}

.cover-preview-img {
    width: 100%;
    height: 100%;
    object-fit: contain;
    border-radius: 9px;
    display: none;
    background: var(--kcover-surface-alt);
}

.cover-slot.filled {
    border-style: solid;
    border-color: var(--kcover-primary);
    padding: 0;
    overflow: hidden;
}

.cover-slot.filled .empty-state {
    display: none;
}

.cover-slot.filled .cover-preview-img {
    display: block;
}

.change-btn {
    position: absolute;
    bottom: 10px;
    right: 10px;
    background: rgba(2, 6, 23, 0.62);
    color: #fff;
    width: 32px;
    height: 32px;
    border-radius: 50%;
    display: flex;
    align-items: center;
    justify-content: center;
    cursor: pointer;
    opacity: 0;
    transition: 0.2s ease;
    z-index: 10;
}

.cover-slot:hover .change-btn,
.pdf-slot:hover .change-btn {
    opacity: 1;
}

.change-btn:hover {
    background: rgba(2, 6, 23, 0.82);
    transform: scale(1.08);
}

.connector-plus {
    font-size: 2rem;
    color: var(--kcover-border);
    display: flex;
    flex-direction: column;
    align-items: center;
    gap: 5px;
}

.pdf-slot {
    width: 260px;
    aspect-ratio: 1 / 1.414;
    background: var(--kcover-surface-alt);
    border: 3px dashed var(--kcover-border);
    border-radius: 12px;
    position: relative;
    cursor: pointer;
    transition: all 0.25s ease;
    display: flex;
    flex-direction: column;
    align-items: center;
    justify-content: center;
    box-shadow: var(--kcover-shadow);
}

.pdf-slot::before {
    content: '';
    position: absolute;
    top: 4px;
    right: -8px;
    bottom: 4px;
    width: 100%;
    background: var(--kcover-surface);
    border-radius: 12px;
    border: 1px solid var(--kcover-border);
    z-index: -1;
    transform: rotate(2deg);
}

.pdf-slot::after {
    content: '';
    position: absolute;
    top: 8px;
    right: -16px;
    bottom: 8px;
    width: 100%;
    background: var(--kcover-surface);
    border-radius: 12px;
    border: 1px solid var(--kcover-border);
    z-index: -2;
    transform: rotate(4deg);
}

.pdf-slot:hover {
    border-color: var(--kcover-primary);
    transform: translateX(4px);
}

.pdf-slot.dragover {
    border-color: var(--kcover-primary);
    background: var(--kcover-accent-bg);
}

.pdf-slot.filled {
    background: var(--kcover-surface);
    border-style: solid;
    border-color: var(--kcover-primary);
}

.pdf-info {
    display: none;
    text-align: center;
    width: 100%;
    padding: 0 15px;
}

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

.pdf-name {
    font-weight: 600;
    margin-bottom: 5px;
    color: var(--kcover-text);
    word-break: break-all;
    display: -webkit-box;
    -webkit-line-clamp: 2;
    -webkit-box-orient: vertical;
    overflow: hidden;
}

.pdf-meta {
    font-size: 0.85rem;
    color: var(--kcover-muted);
}

.pdf-slot.filled .empty-state {
    display: none;
}

.pdf-slot.filled .pdf-info {
    display: block;
}

.action-bar {
    position: fixed;
    bottom: 0;
    left: 0;
    width: 100%;
    background: var(--kcover-surface);
    padding: 15px 40px;
    border-top: 1px solid var(--kcover-border);
    display: flex;
    justify-content: space-between;
    align-items: center;
    transform: translateY(100%);
    transition: transform 0.3s ease;
    box-shadow: 0 -12px 24px rgba(2, 6, 23, 0.35);
    z-index: 100;
}

.action-bar.visible {
    transform: translateY(0);
}

.status-text {
    font-size: 0.9rem;
    color: var(--kcover-muted);
    display: flex;
    align-items: center;
    gap: 15px;
}

.status-item {
    display: flex;
    align-items: center;
    gap: 8px;
    opacity: 0.55;
    transition: 0.2s ease;
}

.status-item.active {
    opacity: 1;
    color: var(--kcover-text);
    font-weight: 500;
}

.check-icon {
    color: #10b981;
    font-size: 1.1rem;
    transform: scale(0.5);
    transition: 0.2s cubic-bezier(0.175, 0.885, 0.32, 1.275);
    opacity: 0;
}

.status-item.active .check-icon {
    opacity: 1;
    transform: scale(1);
}

.merge-btn {
    background: var(--kcover-primary);
    color: #fff;
    padding: 12px 30px;
    border-radius: 10px;
    border: none;
    font-size: 1rem;
    font-weight: 600;
    cursor: pointer;
    box-shadow: 0 4px 12px rgba(14, 165, 233, 0.3);
    transition: all 0.2s ease;
    display: flex;
    align-items: center;
    gap: 8px;
}

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

.merge-btn:disabled {
    background: #64748b;
    cursor: not-allowed;
    box-shadow: none;
    transform: none;
    filter: grayscale(0.3);
}

@media (max-width: 780px) {
    .assembly-stage {
        gap: 26px;
    }

    .action-bar {
        padding: 12px 16px;
        flex-direction: column;
        align-items: flex-start;
        gap: 10px;
    }

    .merge-btn {
        width: 100%;
        justify-content: center;
    }
}