px, %, em, rem, vw, vh and more.
✍️ 3 exercises + code challenge in this lessonCSS lengths can be absolute or relative.
px (pixels) is the most common absolute unit.
%: relative to the parent element.em: relative to the element's own font size.rem: relative to the root (html) font size, usually 16px.vw / vh: 1% of the viewport width / height.ch: the width of the "0" character; great for limiting line length.calc() mixes units: width: calc(100% - 40px);
Mastering CSS Units helps you write clean and reliable CSS code. Follow standard conventions, test edge cases, and keep logic simple. Try running the code example below and complete the exercises to build confidence.
<style>
div { background: #2563EB; color: white; margin: 6px 0; padding: 6px; }
.px { width: 200px; }
.pct { width: 60%; }
.rem { font-size: 1.5rem; }
.vw { width: 50vw; background: #14B8A6; }
.calc { width: calc(100% - 80px); background: #071A2F; }
.ch { max-width: 30ch; background: #E34F26; }
</style>
<div class="px">200px</div>
<div class="pct">60%</div>
<div class="rem">1.5rem text</div>
<div class="vw">50vw</div>
<div class="calc">calc(100% - 80px)</div>
<div class="ch">max-width: 30ch keeps long lines short and readable.</div>Check what you learned in “CSS Units”.
Set the font size relative to the root element.
p {
font-size: 1.25;
}
What is 1rem when the html font size is 16px?
Make the box half as wide as its parent using a percentage.
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