Header Modification

Hey,

I am trying to change the header since a while, but without big success :/

I do want to have the STICKY header AND sub header with WHITE background and black font color.

When the homepage is open, the social icons are white font, as soon as you scroll down, they are grey and the background is not fully white anymore

I use the demo data to play around.

Can you help me, how I can fix it / find the settings for it?
Thank you!