/* Core Bootstrap 4.3 Collapse CSS */
.collapse:not(.show) {
    display: none;
}

.collapsing {
    position: relative;
    height: 0;
    overflow: hidden;
    transition: height 0.35s ease;
}

    .collapsing.width {
        width: 0;
        height: auto;
        transition: width 0.35s ease;
    }