https://codepen.io/jh3y/pen/jjRezM 

HTML : 

<div class="container">
  <button role="button" tabindex="0" style="--buttonColor: #0088FF;">Boo!<span></span><span></span><span></span><span></span>
    <div aria-hidden="true">Boo!</div>
    <div aria-hidden="true">Boo!</div>
    <div aria-hidden="true">Boo!</div>
    <div aria-hidden="true">Boo!</div>
  </button>
  <button role="button" tabindex="0" style="--buttonColor: #FFAA00;">Boo!<span></span><span></span><span></span><span></span>
    <div aria-hidden="true">Boo!</div>
    <div aria-hidden="true">Boo!</div>
    <div aria-hidden="true">Boo!</div>
    <div aria-hidden="true">Boo!</div>
  </button>
  <button role="button" tabindex="0" style="--buttonColor: #FF7700;">Boo!<span></span><span></span><span></span><span></span>
    <div aria-hidden="true">Boo!</div>
    <div aria-hidden="true">Boo!</div>
    <div aria-hidden="true">Boo!</div>
    <div aria-hidden="true">Boo!</div>
  </button>
  <button role="button" tabindex="0" style="--buttonColor: #FF0033;">Boo!<span></span><span></span><span></span><span></span>
    <div aria-hidden="true">Boo!</div>
    <div aria-hidden="true">Boo!</div>
    <div aria-hidden="true">Boo!</div>
    <div aria-hidden="true">Boo!</div>
  </button>
  <button role="button" tabindex="0" style="--buttonColor: #9911AA;">Boo!<span></span><span></span><span></span><span></span>
    <div aria-hidden="true">Boo!</div>
    <div aria-hidden="true">Boo!</div>
    <div aria-hidden="true">Boo!</div>
    <div aria-hidden="true">Boo!</div>
  </button>
  <button role="button" tabindex="0" style="--buttonColor: #AADD22;">Boo!<span></span><span></span><span></span><span></span>
    <div aria-hidden="true">Boo!</div>
    <div aria-hidden="true">Boo!</div>
    <div aria-hidden="true">Boo!</div>
    <div aria-hidden="true">Boo!</div>
  </button>
</div>

CSS :

*,
*:after,
*:before {
  box-sizing: border-box;
}
:root {
  --bg: #fafafa;
}
body {
  display: flex;
  align-items: center;
  justify-content: center;
  min-height: 100vh;
  background: var(--bg);
  color: var(--bg);
}
.container {
  display: grid;
  grid-template-columns: 1fr 1fr;
  grid-gap: 20px;
}
button {
  --borderWidth: 5;
  --boxShadowDepth: 8;
  --buttonColor: #f00;
  --fontSize: 3;
  --horizontalPadding: 16;
  --verticalPadding: 8;
  background: transparent;
  border: calc(var(--borderWidth) * 1px) solid var(--buttonColor);
  box-shadow: calc(var(--boxShadowDepth) * 1px) calc(var(--boxShadowDepth) * 1px) 0 #888;
  color: var(--buttonColor);
  cursor: pointer;
  font-size: calc(var(--fontSize) * 1rem);
  font-weight: bold;
  outline: transparent;
  padding: calc(var(--verticalPadding) * 1px) calc(var(--horizontalPadding) * 1px);
  position: relative;
  transition: box-shadow 0.15s ease;
}
button:hover {
  box-shadow: calc(var(--boxShadowDepth) / 2 * 1px) calc(var(--boxShadowDepth) / 2 * 1px) 0 #888;
}
button:active {
  box-shadow: 0 0 0 #888;
}
button span {
  -webkit-clip-path: var(--clip);
  bottom: calc(var(--borderWidth) * -1px);
  clip-path: var(--clip);
  left: calc(var(--borderWidth) * -1px);
  opacity: 0.25;
  position: absolute;
  right: calc(var(--borderWidth) * -1px);
  top: calc(var(--borderWidth) * -1px);
  z-index: 1;
}
button span:nth-of-type(1):hover,
button span:nth-of-type(2):hover,
button span:nth-of-type(3):hover,
button span:nth-of-type(4):hover {
  --clip: polygon(0 0, 100% 0, 100% 100%, 0 100%);
  z-index: 2;
}
button span:nth-of-type(1):hover ~ div:nth-of-type(1),
button span:nth-of-type(2):hover ~ div:nth-of-type(2),
button span:nth-of-type(3):hover ~ div:nth-of-type(3),
button span:nth-of-type(4):hover ~ div:nth-of-type(4) {
  --clip: inset(0 0 0 0);
}
button span:nth-of-type(1) {
  --clip: polygon(0 0, 100% 0, 50% 50%, 50% 50%);
}
button span:nth-of-type(2) {
  --clip: polygon(100% 0, 100% 100%, 50% 50%);
}
button span:nth-of-type(3) {
  --clip: polygon(0 100%, 100% 100%, 50% 50%);
}
button span:nth-of-type(4) {
  --clip: polygon(0 0, 0 100%, 50% 50%);
}
button div {
  -webkit-clip-path: var(--clip);
  background: var(--buttonColor);
  border: calc(var(--borderWidth) * 1px) solid var(--buttonColor);
  bottom: calc(var(--borderWidth) * -1px);
  clip-path: var(--clip);
  color: var(--bg, #fafafa);
  left: calc(var(--borderWidth) * -1px);
  padding: calc(var(--verticalPadding) * 1px) calc(var(--horizontalPadding) * 1px);
  position: absolute;
  right: calc(var(--borderWidth) * -1px);
  top: calc(var(--borderWidth) * -1px);
  transition: -webkit-clip-path 0.25s ease;
  transition: clip-path 0.25s ease;
  transition: clip-path 0.25s ease, -webkit-clip-path 0.25s ease;
}
button div:nth-of-type(1) {
  --clip: inset(0 0 100% 0);
}
button div:nth-of-type(2) {
  --clip: inset(0 0 0 100%);
}
button div:nth-of-type(3) {
  --clip: inset(100% 0 0 0);
}
button div:nth-of-type(4) {
  --clip: inset(0 100% 0 0);
}