I am considering you are using SNOW theme
In qa-styles.css fine .qa-a-item-content at around line #1756
Change font-size: 13px to whatever you want
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.