.file-drop-area,
.upload-placeholder {
    position: relative;
    border: 1.5px dashed rgba(96, 127, 214, 0.62) !important;
    border-radius: 22px;
    padding: 34px 28px;
    text-align: center;
    background:
        linear-gradient(180deg, rgba(255, 255, 255, 0.98), rgba(244, 248, 255, 0.98)),
        radial-gradient(circle at 86% 8%, rgba(46, 99, 255, 0.1), transparent 34%),
        radial-gradient(circle at 12% 100%, rgba(29, 182, 217, 0.08), transparent 28%);
    transition: transform 0.22s ease, box-shadow 0.22s ease, border-color 0.22s ease, background 0.22s ease;
    box-shadow:
        0 0 0 1px rgba(255, 255, 255, 0.72),
        0 18px 32px rgba(31, 57, 120, 0.08);
    overflow: hidden;
}

.file-drop-area::before,
.upload-placeholder::before {
    content: '';
    position: absolute;
    inset: 10px;
    border: 1px solid rgba(123, 148, 220, 0.14);
    border-radius: 16px;
    pointer-events: none;
}

.file-drop-area i,
.upload-placeholder i {
    display: inline-flex;
    align-items: center;
    justify-content: center;
    width: 74px;
    height: 74px;
    margin-bottom: 16px !important;
    border-radius: 24px;
    background: linear-gradient(135deg, rgba(46, 99, 255, 0.12), rgba(29, 182, 217, 0.16));
    box-shadow: inset 0 1px 0 rgba(255, 255, 255, 0.7);
}

.file-drop-area p,
.upload-placeholder p {
    position: relative;
    z-index: 1;
    margin: 0;
    color: #4a618e;
    font-size: 1rem;
    line-height: 1.75;
}

.file-input {
    display: none;
}

.file-drop-area:hover,
.file-drop-area.dragover,
.upload-placeholder:hover,
.drag-over {
    border-color: var(--primary) !important;
    transform: translateY(-3px);
    box-shadow: 0 20px 38px rgba(46, 99, 255, 0.14);
    background:
        linear-gradient(180deg, rgba(255, 255, 255, 1), rgba(238, 244, 255, 1)),
        radial-gradient(circle at 86% 8%, rgba(46, 99, 255, 0.12), transparent 34%);
}

.file-label {
    color: var(--primary);
    font-weight: 800;
    text-decoration: underline;
    text-decoration-thickness: 2px;
    text-underline-offset: 4px;
    cursor: pointer;
}

.file-label:hover {
    color: var(--primary-strong);
}

.nav-tabs .nav-link:focus-visible,
.btn:focus-visible,
.btn-merge:focus-visible,
.btn-remove:focus-visible,
.file-label:focus-visible,
.page-action-btn:focus-visible,
.page-thumbnail-card:focus-visible,
.page-checkbox:focus-visible,
.page-checkbox-wrapper:focus-within,
.page-selection .form-check-input:focus-visible {
    outline: 3px solid rgba(46, 99, 255, 0.28);
    outline-offset: 3px;
    box-shadow: 0 0 0 5px rgba(46, 99, 255, 0.12);
}

.file-list {
    margin-top: 18px;
}

.file-item {
    display: flex;
    justify-content: space-between;
    align-items: center;
    gap: 14px;
    padding: 14px 16px;
    border-radius: 16px;
    margin-bottom: 10px;
    border: 1px solid rgba(168, 185, 229, 0.34);
    background: linear-gradient(180deg, #ffffff, #f8fbff);
    box-shadow: 0 8px 18px rgba(35, 49, 79, 0.05);
    transition: transform 0.18s ease, border-color 0.18s ease, box-shadow 0.18s ease, background 0.18s ease;
}

.file-item:hover {
    border-color: rgba(112, 143, 232, 0.48);
    background: linear-gradient(180deg, #ffffff, #f2f7ff);
    box-shadow: 0 12px 24px rgba(35, 49, 79, 0.08);
    transform: translateX(2px);
}

.file-name {
    font-weight: 700;
    color: #253b67;
}

.file-size {
    color: var(--text-muted);
    font-size: 0.9rem;
}

.btn-remove {
    border: none;
    width: 32px;
    height: 32px;
    flex: 0 0 32px;
    border-radius: 50%;
    color: var(--danger);
    background: #fff1f4;
    transition: transform 0.18s ease, color 0.18s ease, background 0.18s ease, box-shadow 0.18s ease;
}

.btn-remove:hover {
    color: #fff;
    background: var(--danger);
    box-shadow: 0 10px 16px rgba(214, 74, 95, 0.24);
    transform: scale(1.06);
}

.feature-action-section {
    display: flex;
    align-items: flex-start;
}

.btn-merge {
    width: 100%;
    min-height: 52px;
    padding: 13px 20px;
    border: 0;
    border-radius: 16px;
    color: #fff;
    font-weight: 800;
    letter-spacing: 0.02em;
    background: linear-gradient(130deg, var(--primary) 0%, #6183ff 60%, var(--accent) 100%);
    box-shadow: 0 14px 26px rgba(46, 99, 255, 0.24);
    transition: transform 0.2s ease, box-shadow 0.2s ease, filter 0.2s ease;
}

.feature-action-section .btn-merge {
    margin-top: 0;
}

.btn-merge i {
    margin-right: 8px;
}

.btn-merge:hover {
    transform: translateY(-2px);
    box-shadow: 0 18px 32px rgba(46, 99, 255, 0.3);
    filter: saturate(1.05);
}

.btn-merge:disabled {
    background: #b9c4db;
    box-shadow: none;
    transform: none;
    filter: none;
    cursor: not-allowed;
}

.loading {
    display: none;
    margin-top: 18px;
    padding: 22px 18px;
    border: 1px solid rgba(165, 185, 234, 0.32);
    border-radius: 18px;
    text-align: center;
    color: #4e618a;
    background: linear-gradient(180deg, rgba(255, 255, 255, 0.92), rgba(244, 248, 255, 0.98));
    box-shadow: var(--shadow-sm);
}

.spinner {
    width: 44px;
    height: 44px;
    margin: 0 auto 12px;
    border-radius: 50%;
    border: 3px solid rgba(46, 99, 255, 0.16);
    border-top-color: var(--primary);
    animation: spin 0.85s linear infinite;
}

@keyframes spin {
    from { transform: rotate(0deg); }
    to { transform: rotate(360deg); }
}