JSFiddle - React, Tailwind, and code Playground

HTML

<button class="button_style"></button>

CSS

.button_style {
  position: relative;
  font-size: 155px;
  color: black;
  line-height: 0;
  padding: 0;
  background: blue;
  width: 80px;
  height: 80px;
}

.button_style::before {
  position: absolute;
  left: 0;
  bottom: 15px;
  content: "";
  width: 100%;
  height: 10px;
  background: black;
}

.button_style::after {
  position: absolute;
  top: 0;
  right: 15px;
  content: "";
  height: 100%;
  width: 10px;
  background: black;
}