problem interpreting the CSS code

Hello,
I noticed an issue concerning the CSS code we can add into the plugin’s settings.

I try to add this:
.dialog-box-inner span:before {
content: 'OUVERTURE : ';
margin-left: -325px;
}
but the CSS code is always replaced by that:
.dialog-box-inner span:before {
content: \'OUVERTURE : \';
margin-left: -325px;
}

Consequently, the CSS isn’t working.
I need to do this fix in CSS because the translation in French isn’t accurate, and translators aren’t very quick or efficient (I’ve sent some translation suggestions, but none have been taken on board so far)
Caroline