I understand that CSS is used to decide about Layout and other styling things on Web Page. and If CSS is at the bottom of the page then everything (html elements, text, image, etc) will be displayed by using Browser's own styling and when browser find our CSS then it redesign pages again for us. It may be called repainting!
So, I understand that it will look very ugly repainting the page and user seeing it (FOUT - Flash of Unstyled Text - as expert named). But still, I want to understand about:
How much time this repainting can take? Approx value! I understand this can depend on content on the page.
What else happen or can happen?
My main concern right now is about using font-awesome CSS file (externally hosted on their own cdn which download css and font files). I want to know what will happen across devices if I place this at bottom of the page or delay its loading ? Currently it is placed on <head> section as
link rel='stylesheet' href='http://netdna.bootstrapcdn.com/font-awesome/4.0.3/css/font-awesome.css' type='text/css' media='screen'
Use Del so that it should not look main part of the question. Main part of the question is about Some CSS at the bottom then What will happen to repaint, Blocking, etc. with measurement given or supported by measurement etc.
In the above case or in case when only part of document will get affected by CSS at the bottom then what will happen? Browser repaint everything, and what else? How much time it can take. Suppose, font-awesome is used at 10 icons placed in <i>.
I am never sure of what actually happens when CSS is at the bottom. So, please if you have any video or image showing flow then please mention here.
Base everything on performance across devices, and off course user experience as well. Thank you.
Update: I got something more for myself and for everyone.
Here is a function (delayLoadCss) Google suggest for css for below-the-fold content. Though, I am not going to go that extreme but what about doing that for Font-Awesome kind of CSS?
In my experience the loading of css will be virtually instantaneous no mater where it appear on the page--except in one instance: what will cause a delay in the browser applying your css is placing your css after a script element that takes time to complete.
This is why it is considered best practice to end your body section with your scripts, that way your page is rendered and styled before the browser commits to crunching through your scripts.
So if you html looks like this:
<head>
<link rel="stylesheet" type="text/css" href="/css/styles.css">
<script>
[long loading js]
</script>
</head>
<body>
... content
<script>
[long loading js]
</script>
</body>
Then your css will still be applied right off.
However if you structure it like this:
<head>
<script>
[long loading js]
</script>
<style>
[css here]
</style>
</head>
<body>
... content
<script>
[long loading js]
</script>
</body>
or even
<head>
<script>
[long loading js]
</script>
</head>
<body>
... content
<script>
[long loading js]
</script>
<style>
[css here]
</style>
</body>
Then your css will not be applied to the document until after the js has completed.
The first is best practice and I recomend keeping style tags out of your document completely, but certainly out of the body of your document. External style sheets placed above you script tags is the way to go... This is true for font awesome's externally hosted css also. The browser should not hang on rendering that unless your link to it appears after a script element that is taking up the browsers attention.
* EDIT *
However this post directly contradicts what I just said.
There are two cascades that occur with CSS.
The small Cascade: this is the parsing of an individual style sheet
The Big Cascade: This is where the browser performs three "small cascades", in this order:
User Agent (the web browser's native stylesheet)
Author (the stylesheet that you write)
User (the stylesheet the end user can write).
Your question is about what would happen if you put styles anywhere but the head. Let's discuss:
The browser has its own native stylesheet sitting in the background
The browser loads your HTML document first
The browser then reads the <head>
the browser loads assets in the <head>
the browser parses the rest of the document, i.e. the <body>. assets and style rules located here will be processed last.
the last <style> block, or the last stylesheet in your document is the one whose styles over ride everything else.
In a nutshell, the browser applies styles in the order in which they are seen. A stylesheet at the footer would make things worse, not better. I can't offer a quantifiable measurement of worse because I don't have your stylesheets or website.
All Browsers have FOUC (or FOUT). The duration of it is based on the speed of the browser and the quality of your stylesheet. A minified stylesheet which applies text styles immediately after the reset, and before other styles, usually has the least amount of FOUC.
The styles in the footer are not blocked from being processed, and they will not block styles in the <head>, either. Styles in the footer are simply processed last.
I appreciate the answer from Jeremythuff, however I would also like to answer as well and hope it helps you.
Approx it will take a time to download CSS file (if not cached and not inlined) + a moment. This moment depends on CPU, GPU, HD speeds (if cached) and content + scripts as you have already mentioned. In real practice you do not want to use [link href="..."/] at the end of body because of download time.
You also do not want to use inline styles, because they are not cached and this is yet another piece of code users will download with html, however, this solution can work with small inline styles. In practice it does not produce blinks.
I recommend the following schema:
HEAD > MAIN CSS > BODY > HTML > ADDITIONAL CSS > SCRIPTS
If scripts change default behavior of elements (for example preventing a link from clicking) I recommend to put scripts in head instead.
Now about fonts. In my opinion using external fonts is a bad practice. But if you want, fonts better to include in head because you probably cannot inline them in style tag. So the download time problem occurs here.
10 icons is nothing for nowadays CPUs even on mobile phones.
My advices are straightforward:
(if across devices, I also think of page weight because of slow mobile networks)
Have large additional css (significant difference between the size of html with and without css) - do not include at the end nor as [style]...[/style] (never caches), neither as [link href="..."] (takes download time).
Have small additional css - try with [style]...[/style] at the end of the body before scripts.
Do not worry about 10 icons rendering, worry about download time for 1st visiting users (for fonts).
Your questions are interesting... But there's a problem:
CSS stylesheets must be placed in the <head>!! (except if they are scooped)
Otherwise, your html markup is invalid. Then, every browser could handle it differently.
Related
In the PageSpeed Insight report for my site, it's listing all of my css files as "render-blocking resources". My css links all look like this:
<link rel="stylesheet" type="text/css" media="all" href="https://example.com/something.css" />
In the documentation, it says <link rel="stylesheet"> tags are listed as render-blocking stylesheets if they don't have a media attribute that matches the user's device. Since my stylesheets all have media="all", why are they getting listed as render-blocking resources?
The documentation is very misleading.
What they are trying to say is they will not flag something as render blocking if you have a media query that matches the users device only (so a max or min width or an orientation for example).
However even then they will flag it under 'critical CSS' and even if they don't flag it, it is still render blocking if that CSS is required for the 'above the fold' content.
Further down the page you linked in your question they explain it slightly better
Another approach to eliminating render-blocking styles is to split up
those styles into different files, organized by media query. Then add
a media attribute to each stylesheet link. When loading a page, the
browser only blocks the first paint to retrieve the stylesheets that
match the user's device.
That part is the important part, they are trying to get you to put your mobile styles in one style sheet, desktop in another so you only load the bear minimum CSS to render the page initially.
What really matters
Ignore all the confusing stuff, here is the simplest way to tackle a few audits at once.
Inline your critical CSS - the only step you really need
Any CSS that is required to render the 'above the fold' content should be inlined within your HTML within a style tag.
I will warn you, this is difficult, none of the tools out there do this perfectly and it must have every single style rule included to work. (e.g. if you missed just one class that is required to render something 'above the fold' the browser will wait for the style sheet that contains that rule to be loaded and block the rendering.)
Designing for this from the start is the best option
I keep all my 'above the fold' styles in a separate file and inline them at runtime.
I split these files into 2 types - global (site header, general styles used on multiple pages above the fold etc.) and page-specific (e.g. hero for home page, form styling for contact forms etc... whatever is 'above the fold' on each page that is unique enough to not add to the global above the fold styles.)
This will deal with render blocking resources, critical request chains (for CSS) and give you super fast First Contentful Paint and First Meaningful Paint.
Then you just do as they suggest having styles for mobile and desktop separate and make sure you remove unused CSS if you can (yet again a very difficult task so best to design for it from the start).
i want to eliminate the render blocking from my website, but i can't.
I don't use external css files, or fonts, only just a big css file.
When i copyall content from css file in head AllcontentCSS, render blocking disappear from Google Page Insights
Is there a way to eliminate render blocking and include the css file with link in head instead to copy all css in style tag or is good to insert the css in body tag?
You are most likely looking for:
<link rel="stylesheet" href="yourFile.css" media="none" onload="if(media!='all')media='all'">
But, before you proceed, please read the following resources detailing the technique and its limitations:
initial article by Keith Clark
follow up by Taylor Hunt.
Make sure you also go through the links provided by Taylor Hunt. You probably want to use loadCSS function/polyfill from Filament Group.
But be aware this technique will cause FOUC on your page. You should divide your CSS into two parts:
layout basics (load normally - render blocking),
async styles (load async).
I noticed that if I place <style> inside <body> the css would be applied to all elements after and before <style> tag.
So it looks to me that the css is processed when the page is loaded, similar behavior to javascript document ready event. Am I right? And if that is the case in which order would multiple <style> tags be processed?
TL;DR:
In short, the answer to your question is: once a <style> tag is met inside <body> everything stops and the CSSOM is being rebuilt and re-applied to all existing rendered (painted) content.
Placing <style> tags inside <body> is considered bad practice because it can create FOUC. But if your <style> tag only contains rules for elements placed after it in DOM, placing it in body is perfectly fine, as no FOUC can happen.
The render process of a page is quite complex. But, overly-simplified, here's what happens
<head> is read and CSSOM is built. All CSS is render blocking, unless explicitly specified otherwise by use of #media queries. The non-blocking CSS is still loaded, it's not entirely skipped.
DOM building and CSSOM building are ran in paralel, but all <script> execution is deferred until CSSOM has been built (on </head> tag met), at which point all loaded <script>s are ran, blocking DOM building. JS can make changes to CSSOM at this point. *
Placing <style> tags inside <body> interrupts everything (JS execution and DOM building), CSSOM is being updated and applied to the already rendered content, if any. Everything is resumed after.
* On further testing it appears <head> parsing is single threaded. CSSOM building does block javascript execution but it's done is stages, as each <link /> and <style> tags are met (a <script> placed after a <link> will only execute after the <link /> was resolved and applied to CSSOM). <script> tags placed in between CSS resources are not deferred until all CSS resources in <head> are parsed, as I initially thought.
And, of course js can make changes to CSSOM at run time. See this question I asked for more on how js execution is blocked by CSSOM building.
All the above apply to the normal loading, without considering async, which adds a whole new layer of complexity to it.
If you're interested in more details, I recommend going through the Performance chapter of Web Fundamentals, provided by Google.
Scope of CSS
A style element applies to the whole document, regardless of its position. It is applied as soon as it's loaded.
Reason for putting style tags in <body>
Since every browser has a limited number of threads for downloading a page's files (like JS, CSS, images and asynchronously loaded HTML, JSON or XML), people tend to include CSS files at the end of the body element instead of the classic approach of including them in the head element. This way the rest of the page can be loaded and rendered, and the styling is applied last. You would go this way if your CSS is purely for the looks (i.e. no required element hiding) in order to improve the user experience.
CSS files vs style rules in HTML
Including an external CSS file or putting the same rules in a style element have equivalent results regarding layout and styling. The external file has the downside of a little HTTP overhead, but the benefit of being cached for any further request. If your site consists of more than one page, you usually want to have one or more CSS files that are downloaded only once and re-used for most pages. In addition you can have page-specific rules in another file or within the HTML page.
So it looks to me that the css is processed when the page is loaded, similar behavior to javascript document ready event. Am I right?
No. The stylesheet is modified with the new CSS code when that code is added to the DOM. There's no delay until the rest of the DOM has finished loading. If there was you'd see a FOUC.
which order would multiple <style> tags be processed?
The order they appear in. Then the normal rules of the cascade apply.
So I was running my site through Google's PageSpeed Insights and it told me that I could improve CSS delivery by delaying loading non-critical resources. In particular it referenced to the inclusion of font awesome:
<link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/font-awesome/4.4.0/css/font-awesome.min.css">
I figured I could delay its load by simply putting it before the scripts before the closing body tag, like so:
...
<link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/font-awesome/4.4.0/css/font-awesome.min.css">
<script src="//ajax.googleapis.com/ajax/libs/jquery/1.11.2/jquery.min.js"></script>
<script src="js/min/scripts.min.js"></script>
</body>
</html>
However! When taking a look at Google's documentation on delivery speed, I found two different solutions.
In my native language (Dutch; you can change the language of the documtnation in the right lower corner) the documentation states that I should place non-essential css below the closing html tag. This seems awefully odd to me. Wouldn't this complicate things when trying to access the file through JS? Why wouldn't you place it before the closing body tag?
...
</body>
</html>
<link rel="stylesheet" href="small.css">
However, in the English documentation things get more complicated and require JavaScript:
...
<script>
var cb = function() {
var l = document.createElement('link'); l.rel = 'stylesheet';
l.href = 'small.css';
var h = document.getElementsByTagName('head')[0]; h.parentNode.insertBefore(l, h);
};
var raf = requestAnimationFrame || mozRequestAnimationFrame ||
webkitRequestAnimationFrame || msRequestAnimationFrame;
if (raf) raf(cb);
else window.addEventListener('load', cb);
</script>
</body>
</html>
Why would JS required? Isn't that a bit over the top?
What is wrong with my approach? Why can't you load non-critical CSS before the closing body tag?
An external stylesheet will block rendering of the page until it has been fully loaded. Google is recommending to place the style that is needed for the initially visible (critical, above the fold) part of the document inside <style> tags in the head (the only place where you can define non-inline style) to avoid this render-blocking. The non-critical style (what you don't directly see when you land on the page) is added as an external stylesheet inside the head after the HTML has been read. This way it's rendered first and only then will all other styles be loaded. All for the sake of showing the visitor the content as quickly as possible and not letting her/him wait any longer than necessary.
It think for most cases it is over the top what Google is recommending and they're just being freaky about a few milliseconds - their approach only makes sense somewhat if the CSS is huge. But I think it's hard, if not near impossible, to maintain with the current tools available. What for example if it is a returning visitor that has scrolled down the page at an earlier point and will automatically land there again (Opera is a browser that is very stubborn with this)? For that alone you'd need more JS and possibly juggle with the styles. That can't be a good way to go. And even for the initial display you'd have to stuff some media queries inside the head directly in order to try and get things right without resorting to full screen sections. That's all quite counterproductive and overcomplicating.
Putting <style> or <link> tags outside the head section might work but it's incorrect. I'm sure Google's not on that standpoint anymore and that the English version is the only valid documentation.
Edit - see comments for a nuance on this.
Even if one does do it the google way and get a 'good' score on PageSpeed Insights that doesn't mean too much. You could still hide the whole page and only show it when everything has been loaded (which isn't unusual) without that effecting the score.
I've personally decided to ignore it until they've implemented a feature where you can load CSS asynchronously (like you can with JavaScript and async already) like is announced in the documentation. It would still require a special use case then but at least you could build a framework for it. Not a fan of plugins for something rather trivial myself.
One important thing is missing in the Google documentation - providing a fallback when JavaScript has been disabled. Luckily with HTML5, <noscript> tags can be used for this :
<head>
/* other stuff */
<noscript><link rel="stylesheet" href="small.css"></noscript>
</head>
Sidenote - Google's own analytics script will prevent a perfect PageSpeed score because of the (logically) quick cache expiration they've set on it. Figure that.
I'd suggest you have a look at this repository: https://github.com/filamentgroup/loadCSS
LoadCSS is a very savvy script by the people at Filament Group to lazyload stylesheets in a way, that most browsers play along nicely.
If Javascript is disabled or for whatever reason the script won't work, there are fallbacks included as well.
To answer your specific questions:
Javascript is NOT required to accomplish what you want. There are several methods for loading CSS in a non-blocking fashion. Some rely on JS, some do not. Filamant Group's LoadCSS is a JS option. Critical Path's CSS Generator is one non-JS method. The process of generating the critical CSS can also be automated using Gulp or Grunt.
While your method will work it's not recommended. Google recommends loading the non-critical CSS files using Javascript so the CSS is loaded into the head after the page has finished loading.
Alternatives
There are 2 ways to improve your current implementation.
It sounds like you're currently loading 2 CSS files - your site's CSS, and font-awesome.min.css. This requires 2 HTTP requests and will cause a small delay. Combine the CSS from the 2 files into a single CSS file.
As the others have pointed out Google recommends inlining the critical CSS into the head of the page, and loading the remaining CSS in a non-blocking way. An alternative option I've found useful is to load the entire contents of the CSS into the head of the site within a style tag. I recommend this only if your CSS file is relatively small and minimized.
<head>
<style>
// ALL YOUR CSS
</style>
</head>
I think you are focusing on the wrong part of their (confusing) documentation. I think what they really are trying to share, is that you should put your critical CSS inlined into your html. Look at the blue class in the style tag
<html>
<head>
<style>
<!-- This is what they are trying to show -->
.blue{color:blue;}
</style>
</head>
<body>
<div class="blue">
Hello, world!
</div>
<script>
var cb = function() {
var l = document.createElement('link'); l.rel = 'stylesheet';
l.href = 'small.css';
var h = document.getElementsByTagName('head')[0]; h.parentNode.insertBefore(l, h);
};
var raf = requestAnimationFrame || mozRequestAnimationFrame ||
webkitRequestAnimationFrame || msRequestAnimationFrame;
if (raf) raf(cb);
else window.addEventListener('load', cb);
</script>
</body>
</html>
I read the same documentation in french, which seems to be as outdated as your dutch version and here again, they placed the blue class inlined
<html>
<head>
<style>
.blue{color:blue;}
</style>
</head>
<body>
<div class="blue">
Hello, world!
</div>
</body>
</html>
<link rel="stylesheet" href="small.css">
What they are trying to tell, is that critical CSS can be put directly in html without loading the whole CSS file. In their example, the blue class is critical since it is the only one used.
Concerning the outside of the html tag, It is indeed invalid HTML, but browsers seems to allow it anyway. For the JS code part I guess they are trying to add the stylesheet in the header, but only when the JS will be executed, which mean at the end of the page load. At this point, you might want to think about code readability over performance.
Well, there are 3 main sections, where You can place
first is body, second is head and third is everywhere in html, try to work with it
I am new in css. My project is Layout Manager. Most of the time I use inline css. When I showed my project to the project head, he said to reduce inline css.
Is inline css really bad for project? Please help to clear my vision.
Inline CSS is bad, period. It does not matter which framework you're using. In addition to bloating the document (and potentially slowing load time), it also makes it a lot harder to figure out where the heck values are being set -- as a general rule HTML is dynamic and CSS rarely is. This means if you want to change a style value, you are probably looking at one, flat CSS file, instead of a potentially massive codebase.
I am new in css
No, you are new to wweb programming. You can not say you did HTML etc. without touching CSS at all ;)
My project is Layout Manager
Which tells us nothing.
Is inline css really bad for project?
no, it has zero implications for your project.
It normally is a maintenance problem (not if auto generated). It's main issue is waste of bandwidth because inline CSS have to be on every page instead of being on a seaprate file loaded only once for all pages in the site. Dependingon size and traffic this can be SIGNIFICANT.
the reasons why should avoid inlines css
a) Separation of concerns - your markup should contain only markup code and all you rhutehr hunky dory code should be in separate files like js and css.One of the main goals of CSS is to remove the design elements from the HTML and place them in another location for the designer to maintain. That means that a designer doesn't have to also be the content developer to maintain the look of the Web site.
b) Caching of Files when you have your js and css in separate files the browsers starts caching this till something has changed on the server and this means less data transmitted between the server and the client thus saving up on b/w and the page loading faster for your viewers..
c)Make maintenance easy
One of the most forgotten elements of Web design is the maintenance. Things change - from the look of your site to the content and links within it. And having your CSS in a central place makes it that much easier to maintain.
d)Keep your site accessibile
Using CSS styles can keep your site more accessible both to disabled people and to robots like search engines.
e)Your site will stay current longer
By using best practices with your CSS, you're using standards that have been proven to work and remain flexible as the Web design environment changes.
In this case the style will be loaded before the page loads.
<html>
<head>
<link href="style.css" rel="stylesheet" type="text/css" />
</head>
<body>
<div class="anyClass">Hello</div>
</body>
</html>
But if we use the following, browser will be interrupted during parsing every specific style defined inline the style attribute, so this will slowdown load-time:
<html>
<body>
<div style="height: 70px;">Hello</div>
</body>
</html>
Also, placing the style in a separate style-sheet will help you reusing the styles and maintenance of the code will be easier.
Inline CSS is bad or good depending on what you will achieve in the project in the future.
For example take this two general cases:
If the css that you define inline will be used again then using inline is bad, just add it to a css file and reuse it every time you need in the future.
If the inline you are using is an one time exception then it is a good solution and there is no point in overcomplicating design by placing it in a separate css file.
It is a good practice to separate HTML, css and javascript in separate files and because you are new to web programming, you can make this practice easily from the beginning.
The disadvantages of inline CSS are:
Significant usage of bandwidth.
Cannot use a style on multiple documents.
Cannot implement pseudo-elements and pseudo-classes in inline styles.
Cannot create neat and clean HTML with inline css.