HTMLify

:root {
  --accent: #04da97;
  --border-width: 3px;
  --border-radius: 55px;
  --font-size: 30px;
}

* {
  margin: 0;
  padding: 0;
}


body {
  height: 100vh;
  display: grid;
  place-items: center;
  background-color: #151515;
  font-family: sans-serif;
}

.container {
  perspective: 800px;
}

.toggle {
  position: relative;
  border: solid var(--border-width) var(--accent);
  border-radius: var(--border-radius);
  transition: transform cubic-bezier(0, 0, 0.3, 2) 0.4s;
  transform-style: preserve-3d;
  perspective: 800px;
}

.toggle>input[type="radio"] {
  display: none;
}

.toggle>#choice1:checked~#flap {
  transform: rotateY(-180deg);
}

.toggle>#choice1:checked~#flap>.content {
  transform: rotateY(-180deg);
}

.toggle>#choice2:checked~#flap {
  transform: rotateY(0deg);
}

.toggle>label {
  display: inline-block;
  min-width: 170px;
  padding: 30px;
  font-size: var(--font-size);
  text-align: center;
  color: var(--accent);
  cursor: pointer;
}

.toggle>label,
.toggle>#flap {
  font-weight: bold;
  text-transform: capitalize;
}

.toggle>#flap {
  position: absolute;
  top: calc(0px - var(--border-width));
  left: 50%;
  height: calc(100% + var(--border-width) * 2);
  width: 50%;
  display: flex;
  justify-content: center;
  align-items: center;
  font-size: var(--font-size);
  background-color: var(--accent);
  border-top-right-radius: var(--border-radius);
  border-bottom-right-radius: var(--border-radius);
  transform-style: preserve-3d;
  transform-origin: left;
  transition: transform cubic-bezier(0.4, 0, 0.2, 1) 0.5s;
}

.toggle>#flap>.content {
  color: #151515;
  transition: transform 0s linear 0.25s;
  transform-style: preserve-3d;
}