Simple CSS library to change font size using classes.
Include the following in your HTML:
<link rel="stylesheet" type="text/css" href="https://cdn.jsdelivr.net/gh/hugonun/fsize/fsize.css">
Now simply include the class size with the desired size in the HTML tag. The size can be from 0px to 256px.
Example:
<p class="size12">Hello world</p>