Sometimes you will want to add additional styles or CSS to your WordPress website. These additional rules can override what your theme says and make changes site wide.
In this example we want to fix the width of the buttons on screen so they are all the same width.
In the WordPress dashboard goto [Appearance] [Customise]
Scroll down to the bottom of the left hand menu and click [Additional CSS]
Then past or type your additional CSS rules
Click [Publish] at the top left of the screen to save your changes.