JSFiddle - React, Tailwind, and code Playground

HTML

<div id="test"></div>

CSS

html {
  background: red;
}

#test {
  position: absolute;
  bottom: 0;
  left: 0;
  right: 0;
  height: 150px;
  background: blue;
}

#test::before {
  content: "";
  border-top-left-radius: 50%;
  border-top-right-radius: 50%;
  background: red;
  position: absolute;
  top: 0px;
  height: 100px;
  width: 100%;
  transform: rotate(180deg);
}