This add-on allows you to set the font size of the UI in Anki 2.1.x. Go to Tools > Add-ons > Set Font Size > Config then change the value of font_size to the desired size (in pixels). Please restart Anki after installing the add-on for the first time.
This add-on was ported from the Increase Font Size add-on for Anki 2.0.x by Damien Elmes. If you would like to contribute, the source repository is available on GitHub.
Check out the page for this add-on on AnkiWeb for installation details.
The source code for this add-on is licensed under the GNU General Public License, version 3. See LICENSE for details.