Need your help outside please all in effort to create landing page

Tell us what’s happening:
hello please can someone help me here, i created container-Holder with division: header, content and footer i gave them the background-color but the footer background-color fails to appear my code in codepen.io

thank you
Your code so far

I am a novice but I know that footer does not recognize the float, so I think it’s why it fails, when I have a float I use

footer {
clear: /* left, right or both */
here we can use left or both