[CSS / HTML] Footer

Hi !

I want to keep my footer at the bottom of the page when the page is too short. I was constantly redirected to this website.

I tried to adapt the code to my theme (a child theme of Sydney), but I cannot get the desired effect : my website

This is the code

/* STICKY FOOTER */
* {
margin: 0;
}
html, body {
height: 100%;
}
.page-wrap {
min-height: 100%;
height: auto !important;
height: 100%;
margin: 0 auto -4em;
}
.site-footer, .push {
height: 4em;
}

I don’t really understand how I am supposed to modify the HTML code either. I thought it was automatically generated by the php functions …

Right now, the more I read, the less I get, could someone help me with it ?

Thank you ! =)