REM calculations and

Mosh explains how to set the base HTML font size to 10px to simplify REM calculations; i.e. coding “font-size: 62.5%;” on the HTML element. So once we do that what’s the sense of using Aren’t all the suggested font-sizes on header elements now rendered inaccurate?

The font sizes at are defined in units relative to the root/html element, so they will be accurate regardless of what you set the html element’s font-size to. In fact, if you change the “Base Size” at type-scale to 10px, you will see that the generated CSS is doing exactly the same thing that Mosh is doing with the html font-size. Here’s that generated CSS:

@import url('');

html {font-size: 62.5%;} /*10px*/

body {
  background: white;
  font-family: 'Poppins', sans-serif;
  font-weight: 400;
  line-height: 1.75;
  color: #000000;

p {margin-bottom: 1rem;}

h1, h2, h3, h4, h5 {
  margin: 3rem 0 1.38rem;
  font-family: 'Poppins', sans-serif;
  font-weight: 400;
  line-height: 1.3;

h1 {
  margin-top: 0;
  font-size: 3.052rem;

h2 {font-size: 2.441rem;}

h3 {font-size: 1.953rem;}

h4 {font-size: 1.563rem;}

h5 {font-size: 1.25rem;}

small, .text_small {font-size: 0.8rem;}