JSFiddle - React, Tailwind, and code Playground

HTML

<div class="bg">
  <div class="bg__header"></div>
  <div class="bg__line"></div>
</div>

CSS

.bg {
  height: 100vh;
  position: relative;
  overflow: hidden;
}

.bg__header {
  background-color: purple;
  position: relative;
  height: 400px;
}

.bg__header:before {
  content: " ";
  position: absolute;
  right: 50%;
  bottom: 0;
  width: 0;
  height: 0;
  border-style: solid;
  border-width: 0 0 400px 400px;
  border-color: transparent transparent white transparent;
  margin-right: -400px;
}

.bg__header:after {
  content: " ";
  position: absolute;
  background-color: white;
  right: 0;
  left: 50%;
  top: 0;
  bottom: 0;
  margin-left: 400px;
}

.bg__line {
  position: absolute;
  background-color: blue;
  height: 200px;
  width: 200%;
  margin-left: -50%;
  top: 600px;
  transform: rotate(-45deg)
}