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HTML

CSS

CSS Base

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JavaScript

Babel includes JSX processing.

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HTML

              
                <div class="content">
  <p>Base font size set at 100%, which usually means 16px.
  </p>
  
  <p>
  All text elements below are child elements in the .content div, which is set at 1.5rem, or 24px.
  </p>
  
  <p>Try commenting out the .content font-size in the CSS to see how it affects the em-sized fonts.
  </p>
  
  <h2 class="em">Headline set at 3em, resulting size 72px</h2>
  
  <h2 class="rem">Headline set at 3rem, resulting size 48px</h2>
  
  <p class="em">
    This paragraph is set at 1.5em, resulting font-size is 36px.
  </p>
  
  <p class="rem">
    This paragraph is set at 1.5rem, resulting font-size is 24px.
  </p>
  
</div>
              
            
!

CSS

              
                html {
  font-size: 100%;
}

.content {
  font-size: 1.5rem;
}

.em {
  border: 2px solid red;
}

.rem {
  border: 2px solid blue;
}

h2.em {
  font-size: 3em;
}
h2.rem {
  font-size: 3rem;
}

p.em {
  font-size: 1.5em;
}

p.rem {
  font-size: 1.5rem;
}
              
            
!

JS

              
                
              
            
!
999px

Console