Font-size: medium/rem

HTML

<div id="inheritedBlock">
  Foobar inherited
</div>
<div id="mediumBlock">
  Foobar medium
</div>
<div id="remBlock">
  Foobar rem
</div>
<div id="halfRemBlock">
  Foobar 0.5rem
</div>

CSS

html
{
  font-size: xxlarge;
}

#mediumBlock
{
  font-size: medium;
}

#remBlock
{
  font-size: 1rem;
}

#halfRemBlock
{
  font-size: 0.5rem;
}