CSS custom changes not rendering correctly

I purchased a WP compatible responsive theme from Envato recently to redesign my company’s web site. However, I’m having issues with the theme’s customization feature. As suggested in the user manual, I should only make custom CSS changes via a custom CSS panel rather than through the style.css file via the edit feature. The custom CSS changes I’m making in the panel are not rendering on my desktop but are rendering on my mobile. I’ve cleared the cache countless times and have check the site on another desktop machine that’s on a separate hosting service. I even temporarily changed the style.css file to see if the changes would render, and they did. I don’t want to permanently change this file since it’s not suggested and could cause problems with updates.

The section titles are suppose to be 50 px. (As an experiment, I set them at this size so the changes would be noticeable). I’ve contacted the developer of the theme and he told me I needed to clear the cache and that there was nothing on his end he could do. I told him I already did this and he repeated that I needed to clear the cache and that his theme’s code was perfect. I’m getting nowhere with him and am about to trash this theme. But I’ve paid $$ for it and have invested many many hours into trying to resolve the situation. Plus, I’m not 100 percent certain it’s with the theme. Could it be with my hosting platform…but then again I checked the site on another desktop, separate hosting environment and same issue. Any suggestions you have would be appreciated. (I’m not a developer but have some knowledge of CSS, very little of PHP.)

https://www.iveyengineering.com/iveyengineeringdev/