Corp Theme Header Logo Problem

Dear SiteOrigin!

I have just installed now the Corp theme.
I almost ready for the Premium purchase, but the Installed theme is NOT same like in your Demo Page!
I have no header logo, just empty white background, If I add a header logo then it was not working.
Could you tell me please how can I get the FULL SAME result like in the SiteOrigin Corp Demo Site?

Thank you so much in advance!

P.S.:

I already did search in the Threads, I already did these CSS codes, but they are not working…
I mean these:

.site-header {
background: url(https://vehiclediagnosticengineer.co.uk/wp-content/uploads/2018/06/office-meeting.jpg) center center no-repeat;
background-size: cover;
}
.site-header.stuck {
background: transparent;
}