We have used a web application called icomoon to create our fonts from SVG icons. The sources can can be found in server/theme/base/fonts/roots_font.json.zip (for the deprecated Roots/Basis theme stack) and server/theme/base/fonts/tfont.json.zip (for the newer Legacy/Ventura) theme stack. Once icons have been added and the font is regenerated, add the outputted font files into the server/theme/base/fonts directory (renaming as necessary) and the resulting SCSS files in the appropriate server/theme/base/scss/icons directory (additional naming changes may need to be done in style.scss).Instructions
Custom theme updates
Any custom themes using the following line of code will need to remove it, otherwise icons will not load. This potentially includes any custom theme that was based on Roots or Basis:
$THEME->parents_exclude_sheets = array( 'base' => array('flexible-icons'), // Delete this line );
You can find instructions on how to use the font icons can be found at in the Flexible Icons API documentation.
Tips and known limitations