_Rules" class="numbered">CSS Style Rules</h3>

<h4 id="CSS_Validity" class="numbered">CSS Validity</h4>

<p>Use valid CSS where possible.</p>

<p>Unless dealing with CSS validator bugs or requiring proprietary syntax, use
valid CSS code.</p>

<p> Use tools such as the
<a href="https://jigsaw.w3.org/css-validator/">W3C CSS validator</a>
to test.</p>

<p>Using valid CSS is a measurable baseline quality attribute that allows to spot
CSS code that may not have any effect and can be removed, and that ensures
pro