How to change color & border radius of hero content image

Hello! My website is https://auxreverie.com. Sorry it's a mess right now. I cannot figure out how to change the color & roundness of the hero content image below: I believe its location in the theme files is template parts > hero-content > post-type-hero.php > 'html-with-bg' on line 38. Since it's php, I have no idea how to edit it. I only want to round out the border edges to 10px, and I'd like to change that black color to #f5f8fa. If anyone could help, I'd be eternally grateful. Thanks in advance! Eva