Hi.
Using Url("[insert url]") in CSS won’t allow the content builder to save.
Example
.pevTop:before {
background-size: 30px 30px;
display: inline-block;
width: 30px;
height: 30px;
content: "";
background-image: url("https://www.google.com/images/branding/googlelogo/2x/googlelogo_color_272x92dp.png");
}
Console throws an Invlaid Json response error shown below: