Huddle landing page with flexbox

How can a i get the " Ready To Build Your Community? " to get on top of the bottom box, with the dark color. I tried using margin, but the dark background always came on top.

Am i writing to much CSS? i'm using the @midia in order to make the page resize for the mobile, but is there an easier way to make it instead of rewriting the same section diffirently to each size.