Hello Wouter,
I recommend never touch any of the css files in the template css folder.
You can activate a custom.css file.
I have described how to do it here:
https://www.joomla51.com/forum/j51-skylar-main-menu-push-to-leftside#reply-43463
I think in Nina its only the heading 4 (H4) that has this gradient colors, right?
The css for the H4 looks like this:
h4 {
display: inline-block;
font-size: 1.2rem;
letter-spacing: .5px;
line-height: 1.6em;
color: var(--h4-color);
background: linear-gradient(to left, var(--primary), var(--secondary));
-webkit-background-clip: text;
-webkit-text-fill-color: transparent;
text-shadow: 0 0 2px rgba(0,0,0,0.1);
}
I would change it like this:
h4 {
background: none;
-webkit-background-clip: inherit;
-webkit-text-fill-color: inherit;
text-shadow: none;
}
and write this to the your custom.css.
Hope this helps.
Regards
Oliver