How to change the entire survey font size? I tried changing the font size through Look & Feel, but it did not work out. The font size of the answer choices are always bigger than the questions. I also tried Rich Content Editor, it did not work out either. Does anyone have a clue about how to do it correctly? Thank you very much!

If the default Qualtrics settings are not working then you can use the custom css to update the font size, add the below code in Look & Feel -> Style -> Custom CSS
.Skin .QuestionText {font-size:25px !important}
.Skin .QuestionBody {font-size:15px !important}

When you click to change the question text, there may be an option that pops up that says "remove formatting" (see the right-most option below). Click that button and it should default back to what you have selected in the Look and Feel options. I believe this issue happens especially when you've copied and pasted the question text into the survey.