This script sets a specific font size to the entire questionnaire.

Instructions

Paste script below in the global script editor you find in Settings:
sections “Surveys”  ->  “Settings” in survey menu  ->  tab “Advanced” on top left  ->  button “Edit script”.

In the example the font size is set to 12px (in red in the script below). The size can be changed editing this value in the script.

<style>
.question-text-style,
.column-text-style,
.response-text-style,
.single-question-responses label,
.grid-question-table,
.question
{font-size:12px !important;}
</style>