I'm implementing a dark theme on my website using tailwind classes. For example:
<tr className="bg-white dark:bg-dark-blue text-left dark:text-white transition-colors duration-300"></>
And for some reason, whenever I change my theme the transition isn't smooth but laggy and stuttering. I've noticed that with the increase of dark-styled elements on the page, the lag has gotten worse.
I'm not sure if this is actually a tailwind problem or a general CSS performance problem in the browser.
UPDATE
After some test I've come to the conclusion that it actually has nothing to do with transitions but with CSS itself.
I have a lot of elements on the page with dark classes set initially and then whenever I change the theme I just add/remove 'dark' class in <html>. I have may be 50 elements on the page which change their text color and background color and all of them are laggy whenever the theme gets changed. The lag is similar to when you have a memory leak or a loop. It stutters then loads all at once and stuff like that.
So I guess my question is how to optimize CSS performance in this case? or overall?
UPDATE 2
According to Performance page in devtools I'm dropping a lot of frames when changing the theme. And it actually feels like I'm getting 5fps. Here is a screenshot of Performance page prnt.sc/Zz6T88ZFs6Fp. I'm not sure how to read it, may be somebody can give some useful info
If anyone has ever faced/solved this problem, I'd greatly appreciate your advice
It may have to do with the critical rendering path. I'd advice you to read this excellent article : Achieving 60 FPS Animations with CSS3.
In a nutshell, if you have css transitions set other than on transform and opacity css properties, your browser has to recalculate the whole layout, which causes stuttering.
I don't use tailwind and it's hard to test my response without example code but I had a very similar problem several years ago when browsers were a little dumb.
I had many classes for color throughout the html and toggled them with jquery. Here's a quick example of how...
$(".red").removeClass("red").addClass("blue");
I determined that, at the time, the problem was that the items were causing repainting for each change.
What I ended up doing was swapping a class on the body:
<body class="blue">
Whatever
Something else
<!-- lots more -->
</body>
And then:
body.blue a {
color: blue;
}
body.red a {
color: red;
}
And that worked beautifully because, as I understood it, the repaint happened all at once... but I'm guessing to even try you'd have to write a lot of stuff on your own instead of using tailwind. Maybe not, so I hope this line of thinking helps even if using tailwind.
Edit: if I had the same problem and couldn't fix it quickly enough I'd fade the body with a quick opacity out and then back in. Complete hack but it might look cool. Not a solution to your real problem but it might help if you can't fix it.
You can go in the dev tools and then go under "network", then you click on "Disable cache".
After a lot of research I've managed to finally find some useful info.
With the help of this article and some info from here I found out that dropping frames is actually not uncommon but usually it is not as intense as in my case.
There are some particular lines in Profile.json (download from Network page), which can help you find the actual reason(s) of dropped frames. Look for unsupportedProperties.
In my case it was {"args":{"data":{"compositeFailed":8224,"unsupportedProperties":["color"]}},"cat":"blink.animations,devtools.timeline,benchmark,rail","id2":{"local":"0x76c803503df8"},"name":"Animation","ph":"n","pid":40040,"scope":"blink.animations,devtools.timeline,benchmark,rail","tid":13280,"ts":166257565931}. For me the reason was that too many elements on the page change their text color. 884 lines of compositeFailed related to 'color' for one theme switch on my page. Only refactor with the help of https://csstriggers.com/ would be effective in my case.
Currently, I don't know actual reasons for compositeFailed apart from that it has to do with color property and blink animation. Any Google devs would be welcome to enlighten me because I can't really find any info about that.
I want a background image on my page (background.png), but some rogue CSS is thwarting me.
I can see that my style.css from line 39 is being overwritten. I would think this is being done by something like style.css. I search and do not find anything but my original desired specification in that file. I can not find out what css is doing the overriding.
I have searched all the css files I can think of for the specified image (bg_p2_28.jpg). I have searched all the css files for background, nothing seems to come up. It is not being specified in the main HTML
I am barely struggling through as a reasonably competent programmer that has not used HTML since the mid 1990's. I am just trying to modify a template I bought.
What techniques can I use, or how do I interpret what I have here shown here to figure out what CSS override is ultimately being pushed into the page?
EDIT:
Adding the !important; works. It feels very dirty for some reason. I do not know why. I have tried following the javascript in, but the debugger is confusing to the uninitiated. Is the Important! a terrible thing to do, or reasonable? I think it would be useful to understand where these are being set in the java code, but when I search the code, I think the values are stored in variable, so can only be caught at run time.
That's coming from the inline style="" attribute.
If you don't see it in the HTML source, it's probably being set by Javascript.
You can right-click the element in the inspector and click Break on Attribute Modifications to find out where.
You could try background: url(src) !important;, not the perfect solution, but i think it will work for you in this case.
The grey element.style means that it's a style attribute directly on the element itself. Any style on an element will override styles from style sheets unless the sytlesheet style is marked with !important
When using IE8 to view IE7 through the developer tool's browser mode feature, I am having an odd recurring problem with CSS. When I make changes to an external stylesheet and then reference that class in the HTML, it's like IE7 won't recognize it at all. If, however, I put that same styling inline, IE7 will obey it. Has anyone heard of this before? Here's a simple example to help illustrate what I'm saying:
External stylesheet:
.bold {
font-weight:bold;
}
Call in HTML:
<p class="bold">My paragraph here</p>
No changes will be effective in IE7, although all other browsers are fine.
If however, I do this:
<p style="font-weight:bold;">My paragraph here</p>
IE7 seems happy. What's the difference? Do I really have to make CSS changes this way, or is there another workaround?
I'm baffled as to what the issue could be. I don't know if the developer tool's browser mode has a quirk and doesn't quite work as a real-life version of IE7 would, or if this is something completely different. I am using IE8 (I can't upgrade to IE9 at this government computer), but I've heard the problem persists with my changes in IE9's browser mode of IE7 too.
We're using ColdFusion to generate the HTML, using an HTML5 doctype (), and I've added a timestamp parameter to the 2 external stylesheet references so the browser is forced to grab a new copy every time.
Any help with this mystery would be hugely appreciated - thank you!
======
For #Stano or anyone else who is interested in recreating the exact problem, here is a stripped down version of it: https://docs.google.com/open?id=0B02DZPpIlMwGSk1VZHRDUHNCTkU (Can click File > Download to get the zip). Notice in IE7, "Photographer" is fine because it has inline styling, but the others aren't picking up anything.
With regards to your comments, you're right in saying that it could be a caching issue, but it could also be an issue with that stylesheet (though it doesn't look like that's the case), another stylesheet, or invalid HTML.
One of the things that I want to correct you on, because I think it may influence your understanding of how CSS and HTML interact, is that class attributes in HTML elements do not call CSS. Rather, CSS rules tell the browser agent how to render things with certain attributes. This is why we are able to use the elements ID, name, groupname, class, and other values to identify which elements to apply which class to.
I mention this because if you have invalid HTML (a missing end tag, a missing arrow, etc.) it can do all sorts of weird things. A few days ago it helped me solve an issue where a misplaced tag was actually causing a script of mine to loop on one of my pages.
Take a quick second and validate your HTML using the W3C Markup Validator.
When I see website starter code and examples, the CSS is always in a separate file, named something like "main.css", "default.css", or "Site.css". However, when I'm coding up a page, I'm often tempted to throw the CSS in-line with a DOM element, such as by setting "float: right" on an image. I get the feeling that this is "bad coding", since it's so rarely done in examples.
I understand that if the style will be applied to multiple objects, it's wise to follow "Don't Repeat Yourself" (DRY) and assign it to a CSS class to be referenced by each element. However, if I won't be repeating the CSS on another element, why not in-line the CSS as I write the HTML?
The question: Is using in-line CSS considered bad, even if it will only be used on that element? If so, why?
Example (is this bad?):
<img src="myimage.gif" style="float:right" />
Having to change 100 lines of code when you want to make the site look different. That may not apply in your example, but if you're using inline css for things like
<div style ="font-size:larger; text-align:center; font-weight:bold">
on each page to denote a page header, it would be a lot easier to maintain as
<div class="pageheader">
if the pageheader is defined in a single stylesheet so that if you want to change how a page header looks across the entire site, you change the css in one place.
However, I'll be a heretic and say that in your example, I see no problem. You're targeting the behavior of a single image, which probably has to look right on a single page, so putting the actual css in a stylesheet would probably be overkill.
The advantage for having a different css file are
Easy to maintain your html page
Change to the Look and feel will be easy and you can have support for many themes on your pages.
Your css file will be cached on the browser side. So you will contribute a little on internet traffic by not loading some kbs of data every time a the page is refreshed or user navigates your site.
The html5 approach to fast css prototyping
or: <style> tags are no longer just for the head any more!
Hacking CSS
Let's say you're debugging, and want to modify your page-css, make a certain section only look better. Instead of creating your styles inline the quick and dirty and un-maintainable way, you can do what I do these days and take a staged approach.
No inline style attribute
Never create your css inline, by which I mean: <element style='color:red'> or even <img style='float:right'> It's very convenient, but doesn't reflect actual selector specificity in a real css file later, and if you keep it, you'll regret the maintenance load later.
Prototype with <style> instead
Where you would have used inline css, instead use in-page <style> elements. Try that out! It works fine in all browsers, so is great for testing, yet allows you to gracefully move such css out to your global css files whenever you want/need to! ( *just be aware that the selectors will only have page-level specificity, instead of site-level specificity, so be wary of being too general) Just as clean as in your css files:
<style>
.avatar-image{
float:right
}
.faq .warning{
color:crimson;
}
p{
border-left:thin medium blue;
// this general of a selector would be very bad, though.
// so be aware of what'll happen to general selectors if they go
// global
}
</style>
Refactoring other people's inline css
Sometimes you're not even the problem, and you're dealing with someone else's inline css, and you have to refactor it. This is another great use for the <style> in page, so that you can directly strip the inline css and immediate place it right on the page in classes or ids or selectors while you're refactoring. If you are careful enough with your selectors as you go, you can then move the final result to the global css file at the end with just a copy & paste.
It's a little hard to transfer every bit of css immediately to the global css file, but with in-page <style> elements, we now have alternatives.
In addition to other answers.... Internationalization.
Depending of the language of the content - you often need to adapt the styling of an element.
One obvious example would be right-to-left languages.
Let's say you used your code:
<img src="myimage.gif" style="float:right" />
Now say you want your website to support rtl languages - you would need:
<img src="myimage.gif" style="float:left" />
So now, if you want to support both languages, there's no way to assign a value to float using inline styling.
With CSS this is easily taken care of with the lang attribute
So you could do something like this:
img {
float:right;
}
html[lang="he"] img { /* Hebrew. or.. lang="ar" for Arabic etc */
float:left;
}
Demo
Inline CSS will always, always win in precedence over any linked-stylesheet CSS. This can cause enormous headache for you if and when you go and write a proper cascading stylesheet, and your properties aren't applying correctly.
It also hurts your application semantically: CSS is about separating presentation from markup. When you tangle the two together, things get much more difficult to understand and maintain. It's a similar principle as separating database code from your controller code on the server side of things.
Finally, imagine that you have 20 of those image tags. What happens when you decide that they should be floated left?
This only applies to handwritten code. If you generate code, I think that it's okay to use inline styles here and then, especially in cases where elements and controls need special treatment.
DRY is a good concept for handwritten code, but in machine-generated code, I opt for "Law of Demeter": "What belongs together, must stay together". It's easier to manipulate code that generates Style tags than to edit a global style a second time in a different and "remote" CSS file.
The answer to your question: it depends...
Using inline CSS is much harder to maintain.
For every property you want to change, using inline CSS requires you to look for the corresponding HTML code, instead of just looking inside clearly-defined and hopefully well-structured CSS files.
The whole point of CSS is to separate content from its presentation. So in your example you are mixing content with presentation and this may be "considered harmful".
In addition to the other answers, another concern is that it violates the recommended Content Security Policy from MDN, https://infosec.mozilla.org/guidelines/web_security#content-security-policy
The justification they use is that inline javascript is harmful, XSS, etc., but it doesn't justify why inline styles should also be disabled. Maybe someone can comment as to why, but until then, I'll just rely on appeal-to-authority and claim: it's a security best practice to avoid inline styles.
Code how you like to code, but if you are passing it on to someone else it is best to use what everyone else does. There are reasons for CSS, then there are reasons for inline. I use both, because it is just easier for me. Using CSS is wonderful when you have a lot of the same repetition. However, when you have a bunch of different elements with different properties then that becomes a problem. One instance for me is when I am positioning elements on a page. Each element as a different top and left property. If I put that all in a CSS that would really annoy the mess out of me going between the html and css page. So CSS is great when you want everything to have the same font, color, hover effect, etc. But when everything has a different position adding a CSS instance for each element can really be a pain. That is just my opinion though. CSS really has great relevance in larger applications when your having to dig through code. Use Mozilla web developer plugin and it will help you find the elements IDs and Classes.
I think that even if you want to have a certain style for one element, you have to consider the possibility that you may want to apply the same style on the same element on different pages.
One day somebody may ask to change or add more stylistic changes to the same element on every page. If you had the styles defined in an external CSS file, you would only have to make changes there, and it would be reflected in the same element in all of the pages, thus saving you a headache. :-)
Even if you only use the style once as in this example you've still mixed CONTENT and DESIGN. Lookup "Separation of concerns".
Using inline styles violates the Separation of Concerns principle, as you are effectively mixing markup and style in the same source file. It also, in most cases, violates the DRY (Don't Repeat Yourself) principle since they are only applicable to a single element, whereas a class can be applied to several of them (and even be extended through the magic of CSS rules!).
Furthermore, judicious use of classes is beneficial if your site contains scripting. For example, several popular JavaScript libs such as JQuery depend heavily on classes as selectors.
Finally, using classes adds additional clarity to your DOM, since you effectively have descriptors telling you what kind of element a given node in it is. For example:
<div class="header-row">It's a row!</div>
Is a lot more expressive than:
<div style="height: 80px; width: 100%;">It's...something?</div>
Inline CSS is good for machine-generated code, and can be fine when most visitors only browse one page on a site, but one thing it can't do is handle media queries to allow different looks for screens of different sizes. For that, you need to include the CSS either in an external style sheet or in an internal style tag.
In-page css is the in-thing at the moment because Google rates it as giving a better user experience than css loaded from a separate file. A possible solution is to put the css in a text file, load it on the fly with php, and output it into the document head. In the <head> section include this:
<head> ...
<?php
$codestring = file_get_contents("styles/style1.txt");
echo "<style>" . $codestring . "</style>";
?>
... </head>
Put the required css in styles/style1.txt and it'll get spat out in the <head> section of your document. This way, you'll have in-page css with the benefit of using a style template, style1.txt, which can be shared by any and all pages, allowing site-wide style changes to be made via only that one file. Furthermore, this method doesn't require the browser to request separate css files from the server (thus minimising retrieval / rendering time), since everything is delivered at once by php.
Having implemented this, individual one-time-only styles can be manually coded where needed.
According to the AMP HTML Specification it is necessary to put CSS in your HTML file (vs an external stylesheet) for performance purposes. This does not mean inline CSS but they do specify no external stylesheets.
An incomplete list of optimizations such a serving system might do is:
Replace image references with images sized to the viewer’s viewport.
Inline images that are visible above the fold.
Inline CSS variables.
Preload extended components.
Minify HTML and CSS.
Personally, I think the hatred of inline css is just ridiculous. Hardcore cult behaviour, people just sheepishly repeat "Separation of concerns!". Yes, there are times where if there is a repeating element and you will need repeated styling to use a class targeted from a CSS file, but most of the time it improves speed of development and CLARITY OF CODE to put the style inline, it's great if I can look at the code and see that there is a custom margin height, it helps me picture the HTML document as a whole, instead of some named class that gives me little insight into which styles will be applied.
So I will be the contrarian here and say that inline css is great and that people who scream at you for using it are just following what they have been told without actually giving it any original unbiased consideration.
Even though I totally agree with all the answers given above that writing CSS in a separate file is always better from code reusability, maintainability, better separation of concerns there are many scenarios where people prefer inline CSS in their production code -
The external CSS file causes one extra HTTP call to browser and thus additional latency. Instead if the CSS is inserted inline then browser can start parsing it right away. Especially over SSL HTTP calls are more costly and adds up additional latency to the page. There are many tools available that helps to generate static HTML pages (or page snippet) by inserting external CSS files as inline code. These tools are used at the Build and Release phase where the production binary is generated. This way we get all the advantages of external CSS and also the page becomes faster.
In addition to other answers, you cant target the pseudo-classes or pseudo-elements in inline CSS
We have created a template-driven artifact generator that provides an include file capability for any kind of text artifact -- HTML, XML, computer languages, unstructured text, DSV, etc. (E.g., it's great for handling common Web or manual page headers and footers without scripting.)
Once you have that and use it to provide "style" tags inside your "head" tag, the "separation of concerns" argument goes away, to be replaced by "we have to regenerate after every change to the template" and "we have to debug the template from what it generates". Those gripes have been around since the first computer language to get a preprocessor (or someone started using M4).
On balance, we think the meta-izing capability of either a CSS file or "style" tags is cleaner and less error-prone than element-level styling. But it does require some professional judgment, so newbies and scatterbrains don't bother.