My knowledge about how CSS rules are assigned to DOM elements by the browser is quite limited. However, I recently found myself pondering this topic in a particular situation that sparked my curiosity. To formalize my thoughts, I have created an HTML snippet like so:
<section>
<div>I want to be blue</div>
<div style="color:green">I am feeling quite confident <p style="font-weight: bold">about my styles</p></div>
<p>I want to be big</p>
</section>
The text's content within the div elements outlines my requirements clearly: The first div MUST be blue, while styling for the second one does not concern me as much since I may use inherited properties or set them through JavaScript. Additionally, the p element should be bold.
To apply these styles, I initially wrote the following CSS code:
section div {
color: blue;
}
section p {
font-weight: bold;
}
This approach worked perfectly fine, but knowing that CSS allows targeting specific elements more precisely, I decided to rewrite the styles as follows:
section > div:first-child {
color: blue;
}
section > p {
font-weight: bold;
}
By doing this, I could selectively target only direct children of the section and achieve the same results, albeit with more specificity. This led me to wonder if such targeted styling actually helps browsers assign CSS rules to elements efficiently.
I believe that browsers check each DOM element for matching CSS rules, resolve conflicts, and perform necessary overrides based on specificity. Would targeting elements more specifically aid browsers in assigning styles faster (thus increasing performance)? If so, is the impact significant enough to warrant attention? Conversely, would overly specific targeting hinder browser performance, and if so, to what extent?
Your insights on this matter would be greatly appreciated. Thank you!