Use Fira Sans in Kirby’s Panel. See https://github.com/mozilla/Fira for more information on the font.

Put the files in the assets folder in the assets folder of your Kirby installation. Then add the following line to you config.php file:

c::set('panel.stylesheet', 'assets/css/custom-panel.css');

Iksi, https://www.iksi.cc/