To set the height of an HTML element, you can use CSS. The height property defines the vertical size of an element. Here’s a quick example of how to set the height of a <div> using CSS:

css .box { height: 200px; background-color: lightblue; }

This would create a <div> that is 200 pixels tall. You can also use percentages if you want the height to be relative to its parent element:

css .parent { height: 500px; }

.child { height: 50%; / This will be 250px if parent is 500px / background-color: lightgreen; }

If you want the element height to adjust based on the viewport, use the vh (viewport height) unit:

css .responsive { height: 50vh; / This will be 50% of the viewport height / }

Copy<div class="box"></div>
<div class="parent">
    <div class="child"></div>
</div>
<div class="responsive"></div>