Sticky footer with flexbox PS1761

[jackflyer]

Hi,

I don't manage to make my footer sticky as explained on this page (the method called "There is flexbox"), on PS 1.7.6.1 with classic theme (modified). 

The footer stay at the middle of the page when content is small. 

I added the below code to custom.css:

body {
  display: flex;
  min-height: 100vh;
  flex-direction: column;
}
#wrapper {
  flex: 1 0 auto;
}
#footer {
  flex-shrink: 0;
}

the corresponding wrapper is line ~55 of layout-both-columns.tpl
footer is line ~95 of the same file. 

Could someone try to do the same thing so that I know if something is broken on my side or if we can find a solution together ?
Thank you