CSS

Cutting the mustard with only CSS

JavaScript can be pretty brittle, so having a way to exclude browsers that don’t cut the mustard via CSS can be really useful, especially if you don’t want to serve them large amounts of CSS that they won’t properly understand. Since we can’t prevent loading a stylesheet via feature queries, the media attribute on a <link> element seems the next best thing. Andy Kirk has come up with a few combinations:

HTML

<!--
    Print (Edge doesn't apply to print otherwise)
    IE 10, 11
    Edge
    Chrome 29+, Opera 16+, Safari 6.1+, iOS 7+, Android ~4.4+
    FF 29+
-->
<link rel="stylesheet" href="your-stylesheet.css" media="
    only print,
    only all and (-ms-high-contrast: none), only all and (-ms-high-contrast: active),
    only all and (pointer: fine), only all and (pointer: coarse), only all and (pointer: none),
    only all and (-webkit-min-device-pixel-ratio:0) and (min-color-index:0),
    only all and (min--moz-device-pixel-ratio:0) and (min-resolution: 3e1dpcm)
">
 
<!--
    Print (Edge doesn't apply to print otherwise)
    Edge, Chrome 39+, Opera 26+, Safari 9+, iOS 9+, Android ~5+, Android UCBrowser ~11.8+
    FF 47+
-->
<link rel="stylesheet" href="your-stylesheet.css" media="
    only print,
    only all and (pointer: fine), only all and (pointer: coarse), only all and (pointer: none),
    only all and (min--moz-device-pixel-ratio:0) and (display-mode:browser), (min--moz-device-pixel-ratio:0) and (display-mode:fullscreen)
">

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Learn web development on the Mozilla Developer Network

Welcome to the MDN Learning Area. This set of articles aims to provide complete beginners to web development with all they need to start coding simple websites.

The aim of this area of MDN is not to take you from “beginner” to “expert” but to take you from “beginner” to “comfortable”. From there you should be able to start making your own way, learning from the rest of MDN and other intermediate to advanced resources that assume a lot of previous knowledge.

If you are a complete beginner, web development can be challenging — we will hold your hand and provide enough detail for you to feel comfortable and learn the topics properly. You should feel at home whether you are a student learning web development (on your own or as part of a class), a teacher looking for class materials, a hobbyist, or someone who just wants to understand more about how web technologies work.

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Old browsers are not your fault, but they are your responsibility

The fact old browsers exist is not your fault. Don’t start these discussions by acting as if it is your failing that you can’t get the site looking identical in all browsers released in the last 10 years, while using technology only released this year. It’s not your fault, but it is your problem. It is your problem, your responsibility as a web professional to get yourself into a position where you can take the right course of action for each project.

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How to determine which, if any CSS rules are unused on a site

So this is a really interesting way to determine which, if any CSS rules are unused in a stylesheet, site-wide:

Part of this story could certainly be about deleting CSS that is determined to be “unused” in a project. I know there is incredible demand for this kind of tooling. I feel like there are some developers damn near frothing at the mouth to blast their CSS through some kind of fancy tool to strip away anything unneeded.

[…]

Here’s how one company I heard from was doing it:

  1. They injected a script onto the page for some subset of users.
  2. The script would look at the CSSOM and find every single selector in the CSS for that page.
  3. It would also run a querySelectorAll(“*”) and find every single DOM node on that page.
  4. It would compare those two sets and find all selectors that seemed to be unused.
  5. In order to get the best results, it would fire this script after a random amount of seconds, on a random set of users, in a random set of conditions. Even with this, it needed a lot of data over a long period of time.
  6. After that had run for long enough, there was a set of CSS selectors that seemed likely to be unused.
  7. To be sure, unique background images were applied to all those selectors.
  8. After applying those and waiting for another length of time, the server logs were checked to make sure those images were never accessed. If they were, that selector was used, and would have to stay.
    Ultimately, the unused selectors could safely be deleted from the CSS.

Whew! That’s an awful lot of work to remove some CSS.

But as you can imagine, it’s fairly safe. Imagine just checking one page’s CSS coverage. You’ll definitely find a bunch of unused CSS. One page, in one specific state, is not representative of your entire website.

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A Love Letter to CSS

When I tell coworkers of my unabated love for CSS they look at me like I’ve made an unfortunate life decision.

[…]

Sometimes I feel that developers, some of the most opinionated human beings on the planet, can only agree on one thing: that CSS is totally the worst.

[…]

But today I’m going to blow your mind. Today I’m going to try to convince you that not only is CSS one of the best technologies you use on a day-to-day basis, not only is CSS incredibly well designed, but that you should be thankful—thankful!—each and every time you open a .css file.

My argument is relatively simple: creating a comprehensive styling mechanism for building complex user interfaces is startlingly hard, and every alternative to CSS is much worse. Like, it’s not even close.

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The :focus-within pseudo class

The :focus-within pseudo class becomes active when an element itself has focus or if any of its descendants does.

Take for example the following HTML code:

HTML

<div class="container" tabindex="0"> 
  <label for="text">Enter text</label> 
  <input id="text" type="text" /> 
</div>

and the following CSS:

CSS

.container:focus-within { 
  background-color: #aaa; 
}

If the div with the class .container receives focus (it can in this case as it has a tabindex of 0, this is purely for example purposes), it will have a background colour of #aaa.

But it will also have a background colour of #aaa if any of its descendants have the focus. So if the <input> receives focus, then the div’s background will also be #aaa.

This will remove the need for JavaScript that is often used to achieve this effect.

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CSS Ruleset Terminology

An inforgraphic demonstrating the various parts of a CSS rule and their names. See the text following this image for more information.

If you ever wanted a mini-cheat sheet for what every part of a CSS rule is called, here it is:

  • The whole thing is a ruleset.
  • The curly braces and everything inside is a declaration block.
  • The bit before the opening curly brace is a selector.
  • Each key/value pair, as separated by a colon and ending in a semicolon, is a declaration.
  • In those key/value pairs, the key is a property (or property name), and the value is a value (or property value).

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