I understand that you are inquiring about the top bar on your site. If my understanding is correct, you can make the desired modifications by navigating to Customizer > Header > Header Main. Please refer to the screenshot provided here for further reference: https://vertis.d.pr/i/j6BVmQ.
Please let me know if there is anything else I can assist you with.
To add this custom CSS to your WordPress site, Go to Appearance > Customizer > Additional CSS section, Add the CSS code in the text area then click on the “Publish” button.
P.S – You can change the background color to any of your choices.