close #128 | mention why CSS classes are out of scope

Author: riccardoscalco

index.html

@@ -535,7 +535,7 @@ <h1>Maxwell's equations in vacuum.</h1>
 
         <section>
           <h1 id="customisations">Customisations</h1>
-          <p>Rapido focuses on semantic HTML, providing a default style for a variety of HTML elements. Being CSS classes out of scope, authors looking for a different style must opt for a customisation.</p>
+          <p>Rapido focuses on semantic HTML, providing a default style for a variety of HTML elements. Being CSS classes out of scope, authors looking for a different style must opt for a customisation.<small>Rapido does not expose CSS classes. This design choice makes Rapido easier to use and, due to how <a href="https://developer.mozilla.org/en-US/docs/Web/CSS/Specificity#How_is_specificity_calculated">specificity</a> works, easier to extend with custom CSS classes.</small></p>
           <p>You may change the default CSS rules or write new rules that have precedence over the default ones. As usual, this is possible both with <strong>inline declarations</strong> and <strong>stylesheets</strong>. The following examples show some common customisations.
           </p>
           <figure>