Button fontsize adjustment

I can’t get the font size on buttons changed. I read all articles on the forum about the font / button fontsize, but nothing is changing when I add that to the style.css. I found the lines below, but that’s not working.
a.roll-button.button-slider {
_ font-size: 15px;_

I have created a child theme from Sydney, for which the style.css is still empty. I also went through the complete Sydney style.css (from main theme). I adjusted the widget text fontsize there, which resulted in a larger font for my footer widgets, so that’s working. This was just to verify that the site was accepting changes on this file.

Is it possible that the button is from a plugin, and that I need to search there in stead of the Sydney theme? I have a graphical editor named visual composer.

If someone knows, please let me know, thanks !

Hello there,

Which slider type is active on your site? Did you use special configurations? Pleas share a link to your site, to allow me checking it.