Having issues with pseudo elements and content - expected rbrace error

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I am trying to use the pseudo-element ::after to place an icon in a specific area of the page. The CSS I use (which works with every website I've used it on, except for the websites that use cssLint) is as follows:

.gray-text-block::after {content:'\f086';
color: #cdcdcd;
font-size: 70px;
display: inline-block;
position: absolute;
right: 0px;
bottom: 20px;
height: auto;
width: auto;
font-family: fontawesome;
opacity: 0.5;
z-index: 2;}

Every time I try this, it returns the error "Expected RBRACE at line 46, col 35" and changes the CSS to the following:

.gray-text-block::after {content:"/f086";}

So, it is adding unnecessary slashes and quotation marks, which obviously breaks this CSS line. This prevents me from using the ::after selector, which seems counterproductive - does CSSLint do this for all pseudo elements? Because pseudo elements are a mainstay for CSS.

Any thoughts on what I can do to fix this? I am using the Wordpress theme Dzen, which uses CSSLint. Thanks!