<https://xpertdeveloper.com/css-pseudo-class/#webpage>
<http://schema.org/description>
"A pseudo-class is similar to class in HTML. But it's not declared in Markup explicitly. A pseudo-class starts with the colon(:). There is no white space appear between the selector and colon. Also there should be no white space after the colon."
<https://xpertdeveloper.com/css-pseudo-class/>