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CSS Units of Measurement - Absolute vs. Relative| Hitchhikers Platform
What You’ll Learn
In this section, you will learn:
- How to define the absolute size of elements
- How to define the relative size of elements
An important aspect of CSS is defining the size of elements on the page - the
font-size of text, the
width of containers, and the
padding of an element, to name a few examples. There are a few ways you can define these units of measurement. We’ll go through the most common ways below.
Pixels (written as
px in CSS) are used most to define the absolute size of an element. If you define an attribute in pixels, this will not change no matter a user’s screen size. See an example below.
Here, we’re setting the
font-size to be 18px, and the
padding to be 9px. However, this sizing isn’t very flexible - we won’t be able to resize the font & padding to optimize for screen size, nor will users who opt to view elements in large-text for accessibility be able to increase or decrease the size.
Relative sizing allows you to dynamically size components based on a constant value. This allows for a more responsive and accessible design.
rem and em
- rem will size the element relative to the root - aka, whatever the base sizing of your
- em will size the element relative to its parent container.
We’ll typically use
rem in order to keep sizing consistent and relative to the same thing.
See an example below:
This may look exactly the same as the absolute example (because it is!). However, try decreasing your browser width. You’ll notice that the first example stays constant, while the second resizes to be smaller on smaller screens because this page defines the
<html> font-size to be different across screen sizes.
We recommend using
rem whenever possible. You’ll see this appear in Page Builder and Answers CSS.
A common way to indicate the width and height of elements is through percentages. This will indicate the percentage of the parent container that the element should occupy.
For example, in the below example, the container will take 75% of the width of its container.
Try changing this to
33% and see what happens!