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CSS CSS Basics (2014) Understanding Values and Units Em and Rem Units

Posted by sarah shelden
sarah shelden
8,332 Points

ems

Hi!

I understand that an em is relative to the font size. But, what I am confused about is how do you know which font size is being used that it is relative to?

Any assistance would be appreciated!

Thank you

style.css 
/* Complete the challenge by writing CSS below */

header {
  font-size: 1.8em;
}

.title {
  font-size: 1.625em;
}

h1 {
  font-size: 5.625em;
}
index.html 
<!DOCTYPE html>
<html>
  <head>
    <title>Lake Tahoe</title>
    <link rel="stylesheet" href="page.css">
    <link rel="stylesheet" href="style.css">
  </head>
  <body>
    <header>
      <span class="title">Journey through the Sierra Nevada Mountains</span>
      <h1>Lake Tahoe, California</h1>
    </header>
    <div class="main-content">
      <p>
        Lake Tahoe is one of the most breathtaking attractions located in California. It's home to a number of ski resorts, summer outdoor recreation, and tourist attractions. Snow and skiing are a significant part of the area's reputation.
      </p>
      <a href="#">Find out more</a>
      <h2>Check out all the Wildlife</h2>
      <p>
        As spawning season approaches, the fish acquire a humpback and protuberant jaw. After spawning, they die and their carcasses provide a feast for gatherings of mink, bears, and Bald eagles.
      </p>
      <a href="#">See the Wildlife</a>
      <h3>From Tents to Resorts</h3>
      <p>
        Lake Tahoe is full of wonderful places to stay. You have the ability to sleep in the outdoors in a tent, or relax like a king at a five star resort. Here are our top three resorts:
      </p>
    </div>
    <footer>
      <p>All rights reserved to the state of <a href="#">California</a>.</p>
      <a href="#top">Back to top &raquo;</a>
    </footer>
  </body>
</html>

3 Answers

Austin Whipple
Austin Whipple
29,725 Points
Austin Whipple
Austin Whipple
29,725 Points

An em is relative to the font-size of the element being targeted. This makes it a little vague when you ONLY set font sizes with em. However, the font-size of elements cascades down to all children unless overwritten and the default font-size is 16px (unless changed by browser settings). Therefore, 1em generally equals 16px unless it has been changed somewhere in the CSS. The cascading nature of em and its relative-ness can make for some very handy global resets by adjusting body or html font sizes. However, there are a couple things to be aware of with ancestor font sizing. Give this CSS-Tricks article a read for more.

If you're interested in handling measurements with a relative unit, but don't want to deal with cascading changes, give the rem unit a try. The "root em" unit sets measurements with the pixel value of the root (html) element, which as we learned above is 16px unless otherwise modified in the CSS. With rem, you can set all font sizes (and even layout elements) relative to a single value and modify that value with media queries as the browser scales.

sarah shelden
sarah shelden
8,332 Points
sarah shelden
sarah shelden
8,332 Points

Just kidding! Figured it out :)

sarah shelden
sarah shelden
8,332 Points
sarah shelden
sarah shelden
8,332 Points

That makes so much more sense! The default size was confusing me. Thank you!