@landyvlad: Hello there,
Yes, you can style the testimonial section alter font and font size as you want.
But since the theme you are testing Adventurous it does not have a Testimonial Section you will to implement it by using shortcode.

You can check out our newer themes that has a testimonial slider section in the customizer which will look more attractive than a static testimonial text. You can select the testimonial section from the customizer itself and wont have to use shortcodes.

Let me know if this helps you out!
Kind Regards,