Snippets

Performant Parallaxing

Love it or hate it, parallaxing is here to stay. When used judiciously it can add depth and subtlety to a web app. The problem, however, is that implementing parallaxing in a performant way can be challenging. In this article we’ll discuss a solution that is both performant and, just as importantly, works cross-browser.

TL;DR

  • Don’t use scroll events or background-position to create parallax animations.
  • Use CSS 3D transforms to create a more accurate parallax effect.
  • For Mobile Safari use position: sticky to ensure that the parallax effect gets propagated.

[…]

Both Scott Kellum and Keith Clark have done significant work in the area of using CSS 3D to achieve parallax motion, and the technique they use is effectively this:

  • Set up a containing element to scroll with overflow-y: scroll (and probably overflow-x: hidden).
  • To that same element apply a perspective value, and a perspective-origin set to top left, or 0 0.
  • To the children of that element apply a translation in Z, and scale them back up to provide parallax motion without affecting their size on screen.

The CSS for this approach looks like so:

CSS

.container {
  width: 100%;
  height: 100%;
  overflow-x: hidden;
  overflow-y: scroll;
  perspective: 1px;
  perspective-origin: 0 0;
}
 
.parallax-child {
  transform-origin: 0 0;
  transform: translateZ(-2px) scale(3);
}

Which assumes a snippet of HTML like this:

HTML

<div class="container”>
  <div class="parallax-child”></div>
</div>
Source link
Performant Parallaxing | Web | Google Developers
Tags
CSS
Performance
Parallax
CSS - Transforms

Large, custom, accessible checkboxes and radio buttons on GOV.UK

Early in the development of GOV.UK we observed in research how a majority of users would click on radio button or checkbox controls rather than on their labels, despite the fact that the labels are much bigger and therefore easier to click (see Fitt’s Law).

[…]

We reasoned that this was because users didn’t know whether or not they could click on the labels. Many websites don’t let you click on labels, so choosing to always click on the control is perfectly rational user behaviour.

[…]

First we thought we’d try to make it really obvious that you could click our labels, so we coloured them grey and made them respond to the mouse hovering over them.

We thought this would work, so we rolled out the design across services on GOV.UK. We saw again and again though in lab research that most users still clicked on the controls.

[…]

In our latest iteration we’ve replaced the native browser controls with custom ones, which all our supported browsers will get.

We’ve also removed the grey background, as it did not have the effect on user behaviour that it was intended to.

Source link
We've updated the radios and checkboxes on GOV.UK
Tags
Forms
Accessibility
Touch
Forms - Radio buttons
Checkboxes

Using Quantity Queries to write content-aware CSS

CSS

:first-child:nth-last-child(4),
:first-child:nth-last-child(4) ~ * {
  /* Styles here */
}

This asks the question ‘Is this element the first-child and the fourth-last element that I’m working on OR does this element come after the first-child and the fourth-last element that I’m working on?’

Source link
Using Quantity Queries to write content-aware CSS
Tags
CSS
CSS - Selectors
CSS - Layout
CSS - Quantities and children selectors
Content