Why my custom font CSS stopped working?

Hello all,
I'm having some trouble with a CSS code that stopped working and we don't really know why.
This is the code:

@font-face{
font-family: 'San-Serif';
src: url('https://bancatlan1.qualtrics.com/WRQualtricsControlPanel/File.php?F=F_8Dg8pNKAj4Pc2sS');
}
h1, h2, h3, h4, h5, h6, p, div, span, a {
 font-family: 'San-Serif';
}

Somebody know why did this happen? it was working just fine...
In this moment for some reason it displays the correct font on the Look & Feel tab on the little display it has. But on the actual preview link or on the real link, it do not display the correct font.

Thanks!