Why is it a best practice to put CSS tags in the ?
Jun 29, 2025 am 01:21 AM
It is more reasonable to place the <link> tag of CSS in the
area of ??the HTML document, because the browser parses HTML from top to bottom, and puts CSS in will give it priority to download and parse, ensuring that the style is applied during page rendering and avoiding FOUC (no style content flash); although this will block page rendering, it provides a "delayed but stable" experience, which is better than displaying chaotic content first and then adjusting the layout; optimization methods include using media properties, compressing CSS, CDN acceleration, inline critical CSS, etc.; exceptions include asynchronous loading of non-critical CSS, dynamic skinning functions, and advanced means such as automatic loading of build tools in modern front-end frameworks.
Putting the CSS <link> tag in the area of ??an HTML document is a widely recommended best practice. This is mainly done to ensure that the page can apply styles as soon as possible when loading, and improve user perceived performance and overall experience.
Why is it more reasonable to put it in
Browser parsing HTML is a process from top to bottom. When you put CSS's <link> in , the browser will first download and parse these stylesheets, and then render the page content. This can prevent the page from displaying "naked" HTML content first without style (that is, the commonly known as FOUC, flashing without style content).
If you place CSS at the or behind the page, the browser will first render HTML content without styles, and then re-draw the page after the CSS is downloaded. This will cause the page to flicker or layout to shake, and the user experience will be poor.
Will putting it in
Indeed, putting CSS in will cause the browser to pause the rendering of the page while loading the CSS, which looks like a "stumble". But this is actually a "delayed but stable" experience, which is much more comfortable than seeing the messy content first and then getting better.
If you are worried about load blocking, you can optimize it in the following ways:
- Use
mediaattribute to control the loading priority of certain style sheets (such as printing style sheets) - Compress CSS file volume
- Use CDN to speed up resource loading
- Inline critical CSS into
, non-critical parts are lazy loaded
Are there any exceptions?
In some specific scenarios, it may be an option not to put all CSS in , for example:
- Asynchronous loading of non-critical CSS: Some projects delay loading styles that are not used on the first screen to speed up the initial loading speed.
- Dynamic skinning function: Dynamically insert CSS files of different themes through JS, and may not be placed in
at the beginning. - In modern front-end frameworks, CSS may be packaged into components and the loading order is automatically handled by the build tool.
However, these are advanced optimization methods and are not suitable for all projects. For most websites, it is recommended to put the main stylesheet in .
Basically that's it. Although it is not a mandatory requirement, putting CSS is a simple and effective way, which can significantly improve the user's first visit experience.
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