JSFiddle - React, Tailwind, and code Playground

HAML

#mybox
  #closebtn

CSS

#mybox{
position:relative;
top:10px;
background:pink;
width:100px;
height:40px;
}

#closebtn{
  position:absolute;
  bottom:100%;
  right:0;
  height:10px;
  width:10px;
  background:red;
}