JSFiddle - React, Tailwind, and code Playground

HTML

<div class="dropdown-content">
  <div class="triangle"></div>
</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;
   position: relative;
   top: 100px;
}
.triangle {
    position: absolute;
    margin: auto;
    top: -10px;
    left: -160px;
    right: 0;
    width: 15px;
    height: 15px;
    transform: rotate(135deg);
    -webkit-transform: rotate(-135deg);
    -moz-transform: rotate(135deg);
    -o-transform: rotate(135deg);
    -ms-transform: rotate(1355deg);
    border-right: 2px solid #fff;
    border-bottom: 2px solid #fff;
}