An often overlooked website performance bottleneck occurs in the processing of cascading style sheets and the subsequent application of CSS selectors on the document object model of a web page.
To make web pages render faster and improve end-user experience, consider these five CSS performance optimization tips.
1. Use inline styles
If a given style is only used on one specific page element, such as an image slider or carousel, and that component is only used on a few pages of the site, use an inline style at instead of a universally loaded CSS. file. This will not only reduce the size of the external stylesheet, but also the number of CSS selector evaluations that occur on pages that don’t use the component.
2. Use specific styles
Do not apply styles to universal selectors, descendant selectors, and top-level HTML elements. This can trigger many Boolean evaluations. Instead, optimize CSS performance with selections on a finer element, such as a single class style.
3. Optimize CSS with WebComponents
4. Split Your CSS Files
If many of your CSS files are tailored to a specific browser or device, break those styles into multiple CSS files. When running, load only those that are needed.
For example, if mobile and desktop renderings are very different, this can potentially reduce the number of Document Object Model (DOM) evaluations by 50% on each device type.
5. Reduce the size of your DOM
The tricks used to split your CSS file can also be used to reduce the size of your DOM.
Another CSS performance optimization trick is similar to splitting a CSS file into multiple device-specific files. Instead, you can also reduce the size of the web page itself, reduce the number of DOM elements in the HTML, and subsequently speed up client-side rendering.
Style sheets are a modern website developer’s best friend, but they often come with a hidden performance cost. Follow these five CSS performance optimization suggestions and reduce the possibility of your CSS selectors being the performance bottleneck on your website.