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CSS CSS Foundations Values and Units Relative Length Units

About REM

What does it mean when the rem unit's font size is set back to the base font size of the root HTML element?

<!DOCTYPE html>
    <title>Relative Length Units</title>
    <link rel="stylesheet" type="text/css" href="cc1-main-styles.css">
    <link rel="stylesheet" type="text/css" href="style.css">
    <div class="box">
        <h1>Let's use Font-Relative Length Units</h1>
            Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed do eiusmod
            tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam,
            quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo
            consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse
            cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non
            proident, sunt in culpa qui officia deserunt mollit anim id est laborum.
            <a class="more" href="#">Read more...</a>
/* Write your CSS code below */

h1 {
  font-size: 2.5em;

p {
  font-size: 1.5em;

1 Answer

Hugo Paz
Hugo Paz
15,622 Points

Hi Daniel,

I will give you an example:

<div class='main'>

<p class='par'></p>

font-size: 2em;


By default 1em is 16 pixels, and it always relative to the parent element.

So the font in the div main is 32 pixels and the font in the paragraph par inside the div is 96 pixels because its 3 times the font size set in the div.

rem allows you to return to the original value set in the root element.