JSFiddle - React, Tailwind, and code Playground

HTML

<ul class="dropdown-menu"><li><a>--select--</a></li><li><a class="active">ABCD</a></li><li><a >DEFG</a></li><li><a >LMNO</a></li><ul>

CSS

.dropdown-menu {
overflow-y: auto;
height: 300px;
padding: 0 10px;
width: 20px;
margin-right: -20px;
}
.dropdown-menu {
width: 100%;
margin: 2px 0;
}
.dropdown-menu {
font-size: 14px;
}
.dropdown-menu {
margin-top: -1px;
}
.dropdown-menu {
position: absolute;
top: 100%;
left: 0;
z-index: 1000;
display: none;
float: left;
min-width: 130px;
padding: 5px 0;
margin: 2px 9px 0;
list-style: none;
background-color: #ffffff;
border: 1px solid #ccc;
border: 1px solid rgba(0, 0, 0, 0.2);
-webkit-border-radius: 6px;
-moz-border-radius: 6px;
border-radius: 6px;
-webkit-box-shadow: 0 5px 10px rgba(0, 0, 0, 0.2);
-moz-box-shadow: 0 5px 10px rgba(0, 0, 0, 0.2);
box-shadow: 0 5px 10px rgba(0, 0, 0, 0.2);
-webkit-background-clip: padding-box;
-moz-background-clip: padding;
background-clip: padding-box;
}
ul, ol {
padding: 0;
margin: 0 0 10px 25px;
}

ul, ol {
line-height: 15px;
}