JSFiddle - React, Tailwind, and code Playground

HTML

<div class="test">
<button></button>
  </div>

CSS

.test{
  width: 200px;
  height: 300px;
  position: relative;
  background: #ebebeb;
}
.test::after{
  position: absolute;
  width: 100%;
  height: 50px;
  content: "";
  bottom: 0;
  left: 0;
  background: radial-gradient(circle at top, transparent 30px, #6866dd 30px);
}
button{
  position: absolute;
  width: 50px;
  height: 50px;
  background: black;
  border: none;
  border-radius: 50%;
  bottom: 25px;
  left: 75px;
  cursor: pointer;
  background:black;
  z-index:99;
  
}
button::after{
  content: "+";
  color: white;
  font-size: 20px;
  
}