How to add text banner that spans width of page?

I'm attempting to add a text box that spans the entire width of my homepage, directly below the hero banner (see grey text box circled in attached mock-up), that's much shorter than the default section dimensions. It seems like it should be so simple, but...

• If I add a new section, it's much too large 
• If I add a text box to the top of the section directly below the homepage banner, it doesn't have the contrasting gray background I'm going for. I have found the custom code workarounds for changing textbox background colors, but I'm looking for this grey "banner" to span the entire width of the page.

Any help is MUCH appreciated!!

You can add new section then share site url, we can help you reduce section height with code