From QualtricsWiki

Answer Choice Text

Put one or a combination of the following HTML tags around your answer choice text.

To change them all together, use the following:
<font face="Comic Sans MS" color="#CC33FF" size="+2">your text here</font>

To change them individually, remove the other elements:
<font size="+2">your text here</font>
<font face="Comic Sans MS">your text here</font>
<font color="#CC33FF">your text here</font>

Other ways to alter the answer choice text within Qualtrics:
Italicize
<i>answer choice text</i>
Bold
<b>answer choice text</b>
Underline
<u>answer choice text</u>

Entire Survey Text

You can make overall changes to the Look and Feel of the survey through the Look and Feel section.

This should no longer be necessary since the Look and Feel section can be used, but to use CSS to change the answer choice font styles throughout the whole survey, you will need to go to the Header (Edit Survey -> Look and Feel -> Advanced -> Header (edit) -> Source on the toolbar). Copy and paste the item below into the Source of the Header (from "<style type..." to "</style>"). This will change all question and answer choice text.

Edit the information after the colon (:) accordingly, or remove the line of an item you don't need to change.

<style type="text/css">
.SkinInner {
font-family: Arial, Verdana, sans-serif;
font-size: 10pt;
color: red;
font-weight: bold;
}
</style>