in your theme folder open qa-styles.css and search for
background: #ecf0f1 !important;
font-family: "Ubuntu", sans-serif;
just change the font-family inputs but i prefer to remove what you don't need from the fonts list as i did
Welcome to the Q&A site for Question2Answer.
If you have a question about Q2A, please ask in English.
To report a bug, please create a new issue on Github or ask a question here with the bug tag.
If you just want to try Q2A, please use the demo site.