<div class="aspectratio aspectratio__wh">
  4 : 3
  <span class="width">width: 30vw</span>
  <span class="height">height: 30vh</span>
</div>

<div class="aspectratio aspectratio__h">
  4 : 3
  <span class="width">width: auto</span>
  <span class="height">height: 30vh</span>
</div>

<div class="aspectratio aspectratio__w">
  4 : 3
  <span class="width">width: 30vw</span>
  <span class="height">height: auto</span>
</div>
@import url("https://fonts.googleapis.com/css2?family=Exo:wght@600&display=swap");

* {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
}

body {
  width: 100vw;
  min-height: 100vh;
  font-family: "Exo", Arial, sans-serif;
  background-color: #222;
  color: #fff;
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 1.5rem;
  gap: 50px;
}

.aspectratio {
  background-color: #09f;
  display: flex;
  justify-content: center;
  align-items: center;
  position: relative;
}

.aspectratio span {
  position: absolute;
  white-space: nowrap;
}

.width {
  left: 5px;
  right: 5px;
  bottom: calc(100% + 5px);
  text-align: center;
}

.height {
  top: 5px;
  bottom: 5px;
  writing-mode: vertical-lr;
  text-align: center;
  left: calc(100% + 5px);
}

.aspectratio {
  aspect-ratio: 4 / 3;
}

.aspectratio__wh {
  width: 30vw;
  height: 30vh;
}

.aspectratio__h {
  height: 30vh;
}

.aspectratio__w {
  width: 30vw;
}

External CSS

This Pen doesn't use any external CSS resources.

External JavaScript

This Pen doesn't use any external JavaScript resources.