Making Post Titles Boldface Font in Mantra

I can’t for the life of me find the css.style to change all of my post titles to boldface font. I see Mantra has 3 different stylesheets (not counting the mobile stylesheet).

I have looked in all three stylesheet files (style.css, editor-style.css, and editor-style-rtl.css) and did a search for things such as “post” and “post-title” within all 3 of these css stylesheets, but can’t find it, and I don’t see an option within the Mantra Settings in the Appearance>Themes area for making post titles boldface either.

Can you either let me know if (and where) the Mantra setting for this is in the Appearance>Themes area, or let me know what to search for in the css stylesheet (and which stylesheet I should be searching in)? Thanks!

My site is https://beareselleronline.com. However, I have protected all of my posts (each post is a PLR product that I don’t want anyone to have access to yet, until I am ready), so there won’t be any ability to see any post headings. I just basically want them all bolded so they stand out from the post text. Thank you!