JSFiddle - React, Tailwind, and code Playground

HTML

<div class="dropdown-content">
  
</div>

CSS

body{
  background-image: url('//ssl.gstatic.com/gb/images/v1_76783e20.png');
}
.dropdown-content{
 display: inline-block;
 padding: 18px 14px;
 border: 1px solid #ffffff;
 min-width: 160px;
 position: relative;
 box-shadow: 0 0 10px #000000;
 margin: 15px;
}
.dropdown-content:before{
    position: absolute;
    content: "";
    border: 1px solid #ffffff;
    width: 0;
    height: 0;
    border-style: solid;
    border-width: 0 12px 12px 12px;
    border-color: transparent transparent #ffffff transparent;
    top: -12px;
 }