h1,h2,h3 size change in a page with only shortcode

Im trying to change the text heading from h2 to h4 in a couple of pages where there is only shortcode, i.e https://aditmedia.se/5-tips-att-du-ska-lyckas-med-din-affiliatemarknadsforing/ where you leave a comment on a blog post the text is way to big for the text box.

Here is another example where the h2 text is was to big: https://aditmedia.se/annonser/ in my site editor i have only this shortcode: [ads_list]

Please consider that i am a total newbie in html, php, etc

WordPress v 3.9.1 Avada theme 3.4.1

Any ideas please?

Thanks alot.