After reading Louis Lazaris’ insightful article “Those HTML Attributes You Never Use”, I’ve asked myself (and the community) which properties and selectors are lesser-known or should be used more often. Some answers from the community surprised me, as they’ve included some very useful and often-requested CSS features which were made available in the past year or two.
The following list is created with community requests and my personal picks. So, let’s get started!
This is a shorthand property which is often used for resetting all properties to their respective initial value by effectively stopping inheritance, or to enforce inheritance for all properties.
Sets all properties to their respective initial values.
Sets all properties to their inherited values.
Changes all values to their respective default value which is either inherit or initial.
Resulting values depend on the stylesheet origin where this property is located.
Resulting values will match a previous cascade layer or the next matching rule.
aspect-ratio for Sizing Control
When aspect-ratio was initially released, I thought I won’t use it outside image and video elements and in very narrow use-cases. I was surprised to find myself using it in a similar way I would use currentColor — to avoid unnecessarily setting multiple properties with the same value.
With aspect-ratio, we can easily control size of an element. For example, equal width and height buttons will have an aspect ratio of 1. That way, we can easily create buttons that adapt to their content and varying icon sizes, while maintaining the required shape.
I assumed that this issue cannot be fixed, and I moved on. One of the tweets from the community poll suggested that I should look into font-variant-numeric: tabular-nums, and I was surprised to find a plethora of options that affect font rendering.
For example, tabular-nums fixed the aforementioned issue by setting the equal width for all numeric characters.
Render Performance Optimization
When it comes to rendering performance, it’s very rare to run into these issues when working on regular projects. However, in the case of large DOM trees with several thousands of elements or other similar edge cases, we can run into some performance issues related to CSS and rendering. Luckily, we have a direct way of dealing with these performance issues that cause lag, unresponsiveness to user inputs, low FPS, etc.
This is where contain property comes in. It tells the browser what won’t change in the render cycle, so the browser can safely skip it. This can have consequences on the layout and style, so make sure to test if this property doesn’t introduce any visual bugs.
/* child elements won’t display outside of this container so only the contents of this container should be rendered*/
This property is quite complex, and Rachel Andrew has covered it in great detail in her article. This property is somewhat difficult to demonstrate, as it is most useful in those very specific edge cases. For example, Johan Isaksson covered one of those examples in his article, where he noticed a major scroll lag on Google Search Console. It was caused by having over 38 000 elements on a page and was fixed by containing property!
As you can see, contain relies on the developer knowing exactly which properties won’t change and knowing how to avoid potential regressions. So, it’s a bit difficult to use this property safely.
However, there is an option where we can signal the browser to apply the required contain value automatically. We can use the content-visibility property. With this property, we can defer the rendering of off-screen and below-the-fold content. Some even refer to this as “lazy-rendering”.
Una Kravets and Vladimir Levin covered this property in their travel blog example. They apply the following class name to the below-the-fold blog sections.
content-visibility: auto; /* Behaves like overflow: hidden; */
contain-intrinsic-size: 100px 1000px;
With contain-intrinsic-size, we can estimate the size of the section that is going to be rendered. Without this property, the size of the content would be 0, and page dimensions would keep increasing, as content is loaded.
Going back to Una Kravets and Vladimir Levin’s travel blog example. Notice how the scrollbar jumps around, as you scroll or drag it. This is because of the difference between the placeholder (estimated) size set with contain-intrinsic-size and the actual render size. If we omit this property, the scroll jumps would be even more jarring.
Keep in mind that these properties should be used to fix issues once they happen, so it’s safe to omit them until you encounter render performance issues.
CSS evolves constantly, with more features being added each year. It’s important to keep up with the latest features and best practices, but also keep an eye out on browser support and use progressive enhancement.
I’m sure there are more CSS properties and selectors that aren’t included here. Feel free to let us know in the comments which properties or selectors are less known or should be used more often, but may be a bit convoluted or there is not enough buzz around them.