How to hide header title and tagline sitewide?

Hi,
I have a banner with my logo/name and tagline already integrated into the image. I would like to hide these in the customizer, accordingly. I could just leave them blank, but then Google doesn’t have anything to pick up on. So I figure the only option is to put in the text, and find a way to hide it.

People using other themes were told to add this to the Custom CSS plugin:
.headerblock {
display: none;
}

However, it didn’t work for me. I tried about 3 other variations of this. People helping resolve this for other themes also suggested going into “header.php” within the editor to try to change code there, but I was unable to find any of that code. It seems Storefront is somehow unique.

I have the Storefront Designer, if that makes a difference. (I’m really suprised that doesn’t offer this option, and not even the ability to change the size independently. Tons of sites use logos and bake them in, no default text.)

Any help would be really appreciated. Especially in the form of snippets for the CSS customizer, so I don’t have to worry about my changes getting wiped with the next update. Thanks!