&gt;&gt;Quotes are optional in CSS. You should use single quotes as it is visually clearer that the string is not a selector or a style property.<p>&#x2F; * wrong * &#x2F;
.avatar {
  background-image: url(&#x27;&#x2F;img&#x2F;you.jpg&#x27;);
  font-family: &#x27;Helvetica Neue Light&#x27;, Helvetica Neue, Helvetica, Arial;
}<p>&#x2F; * right * &#x2F;
.avatar {
  background-image: url(&#x2F;img&#x2F;you.jpg);
  font-family: Helvetica Neue Light, Helvetica Neue, Helvetica, Arial;
}<p>It looks like their right&#x2F;wrong answers are opposite<p>Edit: It has now been changed, thank you OP! Great list!