HTMLify

:root {
  --primary-light: #8abdff;
  --primary: #6d5dfc;
  --primary-dark: #5b0eeb;
  --white: #ffffff;
  --greyLight-1: #e4ebf5;
  --greyLight-2: #c8d0e7;
  --greyDark: #9baacf;
}

*,
*::before,
*::after {
  margin: 0;
  padding: 0;
  box-sizing: inherit;
}

html {
  box-sizing: border-box;
  font-size: 75;
  overflow-y: scroll;
  background: var(--greyLight-1);
}

body {
  min-height: 100vh;
  display: grid;
  place-items: center;
  background: var(--greyLight-1);
}

.switch input {
  display: none;
}

.switch {
  width: 6rem;
}

.switch label {
  display: flex;
  align-items: center;
  width: 100%;
  height: 3rem;
  box-shadow: 0.3rem 0.3rem 0.6rem var(--greyLight-2),
    -0.2rem -0.2rem 0.5rem var(--white);
  background: rgba(255, 255, 255, 0);
  position: relative;
  cursor: pointer;
  border-radius: 1.6rem;
}

.switch label::before {
  content: "";
  width: 100%;
  height: 100%;
  border-radius: inherit;
  background: linear-gradient(330deg,
      var(--primary-dark) 0%,
      var(--primary) 50%,
      var(--primary-light) 100%);
  opacity: 0;
  transition: all 0.4s ease;
}

.switch input:checked~label::before {
  opacity: 1;
}

.switch label::after {
  content: "";
  position: absolute;
  left: 0.4rem;
  width: 2.1rem;
  height: 2.1rem;
  border-radius: 50%;
  background: var(--greyDark);
  transition: all 0.4s ease;
}

.switch input:checked~label::after {
  left: 57%;
  background: var(--greyLight-1);
}