# Percentage

A size worked out from the parent, so it grows and shrinks with it.

## How do **percentages** work in CSS?

A **percentage** size is worked out from something else, usually the parent element, so the element grows and shrinks with it.

```css
.sidebar { width: 25%; }   /* a quarter of the parent's width */
```

Level: Novice · [More CSS terms at this level](https://www.ask-codey.com/glossary/subjects/css/novice)

Updated: September 27, 2026

Source: https://www.ask-codey.com/glossary/percentage