To change the background image in the home page you need to modify this file: qa-theme/Donut-theme/images/discuss.jpg
Regarding the fonts, the simplest approach would be to modify the CSS according to your needs in this file: qa-theme/Donut-theme/css/donut.css
Welcome to the Q&A site for Question2Answer.
If you have a question about Q2A, please ask here, 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.