font-size 62.5%
Setting the font-size
of the root element (HTML) to 62.5% gives a base value of 10px (assuming that the default browser font size is 16px).
See the Pen font-size: 62.5 by majadc (@majadc) on CodePen.
A bad approach is to set the font-size
of the root element to 10px, as this prevents users from freely scaling the font size in their browser.
See the Pen OJVYYKY by majadc (@majadc) on CodePen.