Check out example codes for "css window height". It will help you in understanding the concepts better.

Code Example 1

div {
    height: 100vh;
}

Code Example 2

.left {
  height: 100vh;
  width: 50%;
  background-color: grey;
  float: left;
}

.right {
  height: 100vh;
  width: 50%;
  background-color: red;
  float: right;
}

Code Example 3

body, html {
  height: 100%;
}

#right {
  height: 100%;
}

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