How to Add Better Discord Themes

Click the settings icon next to your name and number in the bottom left
Locate "Themes" in the Better Discord category on the left hand side
Click on "Themes", where you can now view your available themes as well as the button to open themes folder
To install any themes you have downloaded, simply drag the CSS file into the themes folder that opens when you click "Open Themes Folder"
Toggle your theme and enjoy!