Hello,
It seems that the Styles from the css/dark.css File are getting prioritized which is why it was not working. Please find the following code in the css/custom.css File:
.dark #header.semi-transparent.sticky-header #header-wrap,
#header.dark.semi-transparent.sticky-header #header-wrap { background-color: rgba(0,0,0,0.6); }
and replace it with:
.dark #header.semi-transparent.sticky-header #header-wrap,
#header.dark.semi-transparent.sticky-header #header-wrap,
#header.dark.sticky-header.transparent-header #header-wrap:not(.not-dark) { background-color: rgba(0,0,0,0.6); }
This will definitely fix your issue. Let us know if we can help you with anything else or if you find any further issues.