CSS stylesheets at top or bottom? or How to solve blank page issue?

问题

I have been putting stylesheets on top (between <head></head>) of html. As far as I understand this is the best practice. (e.g. http://stevesouders.com/hpws/css-bottom.php)

Anyhow, recently I have experienced different results. Instead the codes below will return blank page when test.css is slow, which means I am not experiencing progressive rendering.

<!DOCTYPE html>
<html>
<head>
<link rel="stylesheet" href="test.css" />
</head>
<body>
Blah..
</body>
</html>

Then when putting test.css at bottom, I get progressive rendering.

<!DOCTYPE html>
<html>
<head>
</head>
<body>
Blah..
<link rel="stylesheet" href="test.css" />
</body>
</html>

As far as I have understood and tought so far, it should be the other way round.. Probably there are other factors that I have overlooked?

回答1:

Google is fast busting the tradition of styles 'belonging' in the head. They do indeed recommend that critical styling belongs either in the <head> tag or even inline, but that other, non-essential styles should be referenced after the closing </html> tag. This does work on most, if not all modern browsers (I've not tested all).

The reason behind this is to load the bulk of the styles as a non-blocking reference, allowing the browser to begin writing to page before getting all the (potentially) bulky styles. Depending on what's in the 'critical' styles, this could cause an initial layout of hideous proportions before styling is rendered (FOUC). That is probably what you are experiencing with the "blank page" issue.

Remember also that CSS was released almost 20 years ago (1996), so it's not surprising that Google (and others) are manipulating and pushing out the traditional parameters of the concept.

A ridiculously simple example:

<!DOCTYPE html>
<html>
<head>
    <title>It's a Brave New World</title>
    <link rel="stylesheet" type="text/css" href="css/critical_styles.css" />
</head>
<body>
    <!-- best page ever -->
</body>
</html>
<link rel="stylesheet" type="text/css" href="css/bulky_nonessential_styles.css" />

回答2:

CSS should be defined in your <head>.

This way, as elements are loading in the DOM, they will render with the proper styles applied immediately.

回答3:

It is worth remembering that when your browser first loads a CSS file, it usually caches it, although Internet Explorer does not cache CSS files loaded by other files using @import.

So next time around when a page is loaded, the cached version is used with no speed issues. So really, the only issue might occur when a user first loads the page.

I put all my CSS in the <head> where it belongs.

回答4:

Conflicting information can be found all over the internet.

I would strongly suggest that as of today you place only critical CSS as blocking CSS and then the rest as non render blocking using the following method:

    <link rel="stylesheet" href="/path/to/css.css" media="none"  onload="if(media!='all')media='all'">

This will use the media parameter as none which means it will not load at all, and then once the page as loaded onload swap to all thus forcing it to load.

Also read more up about the media attribute here: https://www.w3schools.com/tags/att_link_media.asp

来源：https://stackoverflow.com/questions/8033622/css-stylesheets-at-top-or-bottom-or-how-to-solve-blank-page-issue

标签

css

rendering

progressive