JSFiddle - React, Tailwind, and code Playground

HTML

<div></div>

CSS

@import url('https://fonts.googleapis.com/css2?family=Neucha&display=swap');


* {
  box-sizing: inherit;
}

html {
  box-sizing: border-box;
}

body {
  padding: 50px;
  margin: 0;
  font-family: 'Neucha', cursive;
}

div {
  position: relative;
  width: 200px;
  height: 200px;
  border-radius: 4px;
  background: #fff;
}

div::before {
  content: "";
  position: absolute;
  top: -2px;
  bottom: -2px;
  right: -2px;
  left: -2px;
  border-radius: 5px;
  background: linear-gradient(to top left, pink 30px, transparent 31px, transparent calc(50% - 30px), pink calc(50% - 30px), pink calc(50% + 30px), transparent calc(50% + 30px), transparent calc(100% - 31px), pink calc(100% - 30px) );
  z-index: -1;

}