Leaving footer?

Question

HTML

I decided to try boostrap 3 in the project here. Everything went more or less until I got to the footer.
When resizing to a mobile screen, the footer starts to behave inappropriately. Tell me what could be the problem. My own searches have yielded no results.
Here is a link to an
UPDATE example: if you inspect the footer, you can see that it went up anyway.

Answer 1

problem in .flex-between { ... display: flex; ...}
Removes scrolling justify-content: flex-end;
*unless, of course, that's the problem
+.footer { clear: both; }