Header Background Not Showing

header#site-header {
    background: rgba(255,255,255.7) !important;
    background-color: rgba(255,255,255,.7) !important;
}

To add or override CSS: use the “Additional CSS” option in the customizer. https://codex.www.ads-software.com/CSS#Custom_CSS_in_WordPress

Learn to use the Chrome Developer Tools to help you see and test changes to your CSS.

The header shows a white background for me.
See screenshot:
https://www.awesomescreenshot.com/image/3673940/46cb2a6043bc65abfef35d51e6f92556

The command @sterndata posted corrected the bug. Thank you very much!