JSFiddle - React, Tailwind, and code Playground

HTML

<div class="content">
			<div class="row row-a">
				A
				<div class="sub">
					Sub menu of A<br>
					Sub menu of A<br>
					Sub menu of A<br>
					Sub menu of A<br>
				</div>
			</div>
			<div class="row row-b">
				B
			</div>
		</div>

CSS

div.content {
				-webkit-overflow-scrolling: touch;
			}
						
			div.row {
				width: 100%;
				position: relative;
				background: red;
				margin-bottom: 10px;
			}

			div.sub {
				position: absolute;
				top: 100%;
				z-index: 2;
				background: blue;
			}