Follow these instructions to learn how to change the font and font size for image captions and descriptions:
On the website page, click the gallery.
The settings panel opens on the right side of the Website Builder.
Click the icon to open the Style settings.
Under Image Caption and Image Description, click the drop-down arrows to change the following:
Use the color picker to change font color or apply text highlighting. Please refer to How Do I Use the Color Picker to Change Font Color and Text Highlighting?
Any style changes that you make will apply to all images in the gallery.
Click the icon to close the settings.
The image text is updated with your selections.