Yes, thats possible, but you have to adjust the templates. there is (as far as i know) no ui-way to do this.
Go to layout > pro editor > scroll down to “cascading style sheet” and open the file. assume that you want to change the font size for questions of type 311 add the following text
.type-matrix-311 .title {
font-size:x-large;
color: blue;
}
.type-matrix-311 .subtitle {
font-size:x-large;
color: green;
}
.type-matrix-311 label {
font-size: x-large;
color: red;
}
SAVE the file.
The matrix 311 question contains three parts, title, subtitle and items/labels. so there are three css rules to address each of them. the colors are only there so you can see what part of the question will be changed by this rule. font-size accepts relative sizes like large/x-large or absolute sizes like 16px/20px and so on. you can have a look at MDN to see whats possible there.
