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Image comparison slider with pure CSS

As a few of you know, I have been spending a good part of this year writing a book for O’Reilly called “CSS Secrets” (preorder here!). I wanted to include a “secret” about the various uses of the resize property, as it’s one of my favorite underdogs, since it rarely gets any love. However, just mentioning the typical use case of improving the UX of text fields didn’t feel like enough of a secret at all. The whole purpose of the book is to get authors to think outside the box about what’s possible with CSS, not to recite widely known applications of CSS features. So I started brainstorming: What else could we do with it?

Then I remembered Dudley’s awesome Before/After image slider from a while ago. While I loved the result, the markup isn’t great and it requires scripting. Also, both images are CSS backgrounds, so for a screen reader, there are no images there. And then it dawned on me: What if I overlaid a <div> on an image and made it horizontally resizable through the resize property? I tried it, and as you can see below, it worked!

The good parts:

  • More semantic markup (2 images & 2 divs). If object-fit was widely supported, it could even be just one div and two images.
  • No JS
  • Less CSS code

Of course, few things come with no drawbacks. In this case:

  • One big drawback is keyboard accessibility. Dudley’s demo uses a range input, so it’s keyboard accessible by design.
  • You can only drag from the bottom right corners. In Dudley’s demo, you can click at any point in the slider. And yes, I did try to style ::webkit-resizer and increase its size so that at least it has smoother UX in Webkit. However, no matter what I tried, nothing seemed to work.

Also, none of the two seems to work on mobile.

It might not be perfect, but I thought it’s a pretty cool demo of what’s possible with the resize property, as everybody seems to only use it in textareas and the like, but its potential is much bigger.

And now if you’ll excuse me, I have a chapter to write 😉

Edit: It looks like somebody figured out a similar solution a few months ago, which does manage to make the resizer full height, albeit with less semantic HTML and more flimsy CSS. The main idea is that you use a separate element for the resizing (in this case a textarea) with a height of 15px = the height of the resizer. Then, they apply a scaleY() transform to stretch that 15px to the height of the image. Pretty cool! Unfortunately, it requires hardcoding the image size in the CSS.

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Text masking — The standards way

As much as I like .net magazine, I was recently outraged by their “Texturizing Web Type” article. It features a way to apply a texture to text with -webkit-mask-image, presenting it as an experimental CSS property and misleading readers. There are even -moz-, -o- and -ms- prefixes for something that is not present in any specification, and is therefore unlikely to ever be supported by any non-WebKit browser, which further contributes to the misdirection. A while back, I wrote about how detrimental to our work and industry such proprietary features can be.

A common response to such complaints is that they are merely philosophical and who cares if the feature works right now and degrades gracefully. This argument could be valid for some cases, when the style is just a minor, gracefully degrading enhancement and no standards compliant alternative is present (for example, I’ve used ::-webkit-scrollbar styles myself). However, this is not the case here. We have had a standards compliant alternative for this for the past 11 years and it’s called SVG. It can also do much more than masking, if you give it a chance.

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Better “CSS3 ticket-like tags”

Today I stumbled upon this tutorial, which from the screenshot, looked very interesting. So, I read on, and to my horror I noticed the author suggesting some questionable practices, the worst of which was using 3 HTML elements for every tag, including nonsense markup like <span class="circle"></span>.

So, I thought I’d take a chance at trying to recreate this effect without any extra markup. And it turned out to be quite easy, although using CSS gradients limits browser support a bit (IE10, Firefox 3.6+, Chrome, Safari 5.1).

They have the same disadvantage as the originals: They depend on the background color. However, unlike the originals, they come at less code, they’re scalable without changing a million values (as shown in the “bigger” section) and of course, no extra markup.

You can see the results in the fiddle below:

Disclaimer: webdesign tuts+ occasionally has some nice tutorials. I didn’t write this post to attack them in any way.

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Styling elements based on sibling count

The original idea belongs to André Luís, but I think it could be improved to be much less verbose.

André’s solution is like this:

/* one item */
li:nth-child(1):nth-last-child(1) {
	width: 100%;
}

/* two items */
li:nth-child(1):nth-last-child(2),
li:nth-child(2):nth-last-child(1) {
	width: 50%;
}

/* three items */
li:nth-child(1):nth-last-child(3),
li:nth-child(2):nth-last-child(2),
li:nth-child(3):nth-last-child(1) {
	width: 33.3333%;
}

/* four items */
li:nth-child(1):nth-last-child(4),
li:nth-child(2):nth-last-child(3),
li:nth-child(3):nth-last-child(2),
li:nth-child(4):nth-last-child(1) {
	width: 25%;
}

It’s based on the relationship between :nth-child and :nth-last-child. As you can see, the number of total rules is O(N) and the number of selectors in every rule is also O(N).

However, what you really want, is to just target the first element. The others can be targeted with just a sibling selector. With my improvement, the number of total rules is still O(N), but the number of selectors in every rule becomes just 2, making this trick practical for far larger numbers of children:

/* one item */
li:first-child:nth-last-child(1) {
	width: 100%;
}

/* two items */
li:first-child:nth-last-child(2),
li:first-child:nth-last-child(2) ~ li {
	width: 50%;
}

/* three items */
li:first-child:nth-last-child(3),
li:first-child:nth-last-child(3) ~ li {
	width: 33.3333%;
}

/* four items */
li:first-child:nth-last-child(4),
li:first-child:nth-last-child(4) ~ li {
	width: 25%;
}

And here’s a fiddle to prove it:

Yes, I know that with Flexbox and the other layout modules, techniques such as these are soon becoming obsolete, but I think they are still useful right now.
I’m also aware that you can emulate this particular example with table display modes, but a) Table display modes have other implications that are sometimes undesirable and b) Widths are just an example, you could come up with other ways to style the elements based on their total count, which can’t be emulated by CSS tables.

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CSSNinja’s custom forms revisited to work with CSS sprites

I read today CSS Ninja‘s (Ryan Sheddon’s) brilliant new technique about the creation of custom checkboxes and radio buttons with CSS alone.

The only thing that bugged me about it was something he pointed himself out as well:

This technique has only 1 drawback I can think of, IE support is not a drawback for me, you can’t use a big sprite image to save all the radio and checkbox states, they need to be individual images. Using CSS generated content to insert an image doesn’t give you control of the image position like a background image does.

And then I wondered “but hey, why can’t we use background images?”. It seemed pretty obvious to me that we could combine a transparent text color with normal css sprites and a display of inline-block in the ::before pseudo-element to achieve the exact same effect. I verified that my initial assertion was actually correct, and tested it in Firefox, Chrome, Safari and Opera (the latest only, no time for testing in older ones at the moment) and it seems to work fine.

Here it is: demo | source files (including .psd file of the sprite)

I’m afraid there’s some blatantly obvious drawback in my approach that made Ryan prefer his method over this, but I’m posting it just in case…

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A CSS3 learning(?) tool

In case anyone is interested, this is my take on the “challenge” that Brad Neuberg posted today on Ajaxian. It needs more properties, but it’s very easy to extend. I guess I should also add CSS3 values (RGBA/HSL(A) colors, CSS gradients etc) but oh well, I’m currently in a hurry. I will, if anyone actually finds it useful (?).

It didn’t prove much of a challenge actually and I honestly doubt it’s educational value (actually it’s value in general), but it was an interesting thing to do while drinking my first coffee in the morning — I really enjoyed writing it 🙂