Brine: How customize split color background in an index

Hello! I'm working in Brine and I'm having trouble with my split color background.  The code I'm using works, however, I want the color to extend all the way up to the top of the page—including the header. Right now, the header remains all white. I set the logo and nav to the Bottom—which would normally make the header act transparent and allow the background image/video show thru. The custom CSS I used is throwing something off... or not taking something into account.

Custom CSS currently being used:

/*** SPLIT WELCOME BANNER ***/
#welcome {
background: linear-gradient(90deg, #0814b3 40%, #FFFFFF 0% ); } @media only screen and (max-width: 640px) {#welcome {background: #FFFFFF !important }}

Screenshot:

Website is kaciemclean.com / password: kmtemp01

-----

Follow up questions would be how to make the markdown text, "tiny studio..." to revert to black in mobile view; and how to make logo revert to blue in mobile view/white in desktop view.