<div class="ratio ratio-1-1"><span>1:1</span></div>
<div class="ratio ratio-4-3"><span>4:3</span></div>
<div class="ratio ratio-3-2"><span>3:2</span></div>
<div class="ratio ratio-16-9"><span>16:9</span></div>

html {
  display: flex;
  justify-content: center;
  align-items: center;
  min-height: 100vh;
  color: #ffffff;
  background-color: #121212;
}

body {
  display: flex;
  justify-content: space-around;
  flex-wrap: wrap;
  max-width: 960px;
  margin: auto;
  & > div {
    margin: 1rem;
  }
}

.ratio {
  display: flex;
  align-items: center;
  justify-content: center;
  position: relative;
  width: 200px;
  span {
    position: absolute;
  }
  &::before {
    display: block;
    content: "";
    width: 100%;
    background-color: #AD9CFF;
    border-radius: 10px;
  }
}

/* --- Fun begin here --- */

.ratio-1-1::before {
    padding-top: (1 / 1) * 100%;
    // Equal padding-top: 100%;
}

.ratio-3-2::before {
    padding-top: (2 / 3) * 100%;
    // Equal padding-top: 66.66%;
  }

.ratio-4-3::before {
    padding-top: (3 / 4) * 100%;
    // Equal padding-top: 75%;
  }

.ratio-16-9::before {
    padding-top: (9 / 16) * 100%;
    // Equal padding-top: 56.25%;
  }