Custom.css is not working

Hello,

If I rename the custom-sample.css into custom.css and I change some css in the css file nothing happens. I selected in wordPress the skin “Custom.css” and on my site it keeps the colors background white and font-color orange. Is it possible that a other plugin or my theme overrides the colors of the custom.css and keeps the white and orange colors?

Can someone help me!

Regards,

Levi

https://www.ads-software.com/plugins/shiftnav-responsive-mobile-menu/