The !important CSS Declaration: How and When to Use It

Door globecom op zo, 2014-12-28 14:28

When the CSS1 specification was drafted in the mid to late 90s, it introduced a rule called the !important declaration that would help developers and users easily override normal specificity when making changes to their stylesheets. For the most part, the !important declaration has remained the same, with only one change in CSS2.1 and nothing new added or altered in the CSS3 spec in connection with this unique declaration.

How and When to Use It

Let’s take a look at what exactly this declaration is all about, and when, if ever, you should use it.

[Offtopic: by the way, did you know that we are publishing a Smashing eBook Series? The brand new eBook #3 is Mastering Photoshop For Web Design, written by our Photoshop-expert Thomas Giannattasio.]

A Brief Primer on the Cascade

Before we get into the !important declaration and exactly how it works, let’s give this discussion a bit of context. In the past, Smashing Magazine has covered CSS specificity in-depth, so please take a look at that article if you want a detailed discussion on the CSS cascade and how specificity ties in.

Below is a basic outline of how any given CSS-styled document will decide how much weight to give to different styles it encounters. This is a general summary of the cascade as discussed in the spec:

Find all declarations that apply to the element and property
Apply the styling to the element based on importance and origin using the following order, with the first item in the list having the least weight:
- Declarations from the user agent
- Declarations from the user
- Declarations from the author
- Declarations from the author with !important added
- Declarations from the user with !important added
Apply styling based on specificity, with the more specific selector “winning” over more general ones
Apply styling based on the order in which they appear in the stylesheet (i.e., in the event of a tie, last one “wins”)

With that basic outline, you can probably already see how the !important declaration weighs in, and what role it plays in the cascade. Let’s look at it in more detail.

Syntax and Description

The !important declaration provides a way for a stylesheet author to give a particular CSS value more weight than it naturally has. Here is a simple code example that clearly illustrates how !important affects the natural way that styles are applied:

#example {
font-size: 14px !important;
}

#container #example {
font-size: 10px;
}

In the above code sample, the element with the id of “example” will have text sized at 14px, due to the addition of the !important declaration.

Without the use of !important, there are two reasons why the second declaration block should naturally have more weight than the first: The second block is later in the stylesheet (i.e. it’s listed second). Also, the second block has more specificity (#container followed by #example instead of just #example). But with the inclusion of the !important declaration, the first font-size rule now has more weight.

Some things to note about the !important declaration:

When !important was first introduced in CSS1, an author rule with an !important declaration held more weight than a user rule with an !important declaration; to improve accessibility, this was reversed in CSS2
If !important is used on a shorthand property, this adds “importance” to all the sub-properties that the shorthand property represents
The !important declaration must be placed at the end of the line, immediately before the semicolon, otherwise it will have no effect (although a space before the semicolon won’t break it)
If for some particular reason you have to write the same property twice in the same declaration block, then add !important to the end of the first one, the first one will have more weight in every browser except IE6 (this works as an IE6-only hack, but doesn’t invalidate your CSS)
In IE6 and IE7, if you use a different keyword in place of !important (like !hotdog), the CSS rule will still be given extra weight, while other browsers will ignore it

When Should It Be Used?

As with any technique, there are pros and cons depending on the circumstances. So when should it be used, if ever? Here’s my subjective overview of potential valid uses.

Never

The !important declaration should not be used unless it is absolutely necessary after all other avenues have been exhausted. If you use it out of laziness, to avoid proper debugging, or to rush a project to completion, then you’re abusing it, and you (or those that inherit your projects) will suffer the consequences.

If you include it even sparingly in your stylesheets, you will soon find that certain parts of your stylesheet will be harder to maintain. As discussed above, CSS property importance happens naturally through the cascade and specificity. When you use !important, you’re disrupting the natural flow of your rules, giving more weight to rules that are undeserving of such weight.

If you never use !important, then that’s a sign that you understand CSS and give proper forethought to your code before writing it.

That being said, the old adage “never say never” would certainly apply here. So below are some legitimate uses for !important.

To Aid or Test Accessibility

As mentioned, user stylesheets can include the !important declaration, allowing users with special needs to give weight to specific CSS rules that will aid their ability to read and access content.

A special needs user can add the !important declaration to typographic properties like font-size to make text larger, or to color-related rules in order to increase the contrast of web pages.

In the screen grab below, Smashing Magazine’s home page is shown with a user-defined stylesheet overriding the normal text size, which can be done using Firefox’s Developer Toolbar:

How and When to Use It

In this case, the text size was adjustable without using the !important declaration, because a user-defined stylesheet will override an author stylesheet regardless of specificity. If, however, the text size for body copy was set in the author stylesheet using the !important declaration, the user stylesheet could not override the text-size setting, even with a more specific selector. The inclusion of !important resolves this problem and keeps the adjustability of text size within the user’s power, even if the author has abused the !important declaration.

To Temporarily Fix an Urgent Problem

There will be times when something bugs out in your CSS on a live client site, and you need to apply a fix very quickly. In most cases, you should be able to use Firebug or another developer tool to track down the CSS code that needs to be fixed. But if the problem is occurring on IE6 or another browser that doesn’t have access to debugging tools, you may need to do a quick fix using !important.

After you move the temporary fix to production (thus making the client happy), you can work on fixing the issue locally using a more maintainable method that doesn’t muck up the cascade. When you’ve figured out a better solution, you can add it to the project and remove the !important declaration — and the client will be none the wiser.

To Override Styles Within Firebug or Another Developer Tool

Inspecting an element in Firebug or Chrome’s developer tools allows you to edit styles on the fly, to test things out, debug, and so on — without affecting the real stylesheet. Take a look at the screen grab below, showing some of Smashing Magazine’s styles in Chrome’s developer tools:

How and When to Use It

The highlighted background style rule has a line through it, indicating that this rule has been overridden by a later rule. In order to reapply this rule, you could find the later rule and disable it. You could alternatively edit the selector to make it more specific, but this would give the entire declaration block more specificity, which might not be desired.

The !important declaration could be added to a single line to give weight back to the overridden rule, thus allowing you to test or debug a CSS issue without making major changes to your actual stylesheet until you resolve the issue.

Here’s the same style rule with the !important declaration added. You’ll notice the line-through is now gone, because this rule now has more weight than the rule that was previously overriding it:

How and When to Use It

To Override Inline Styles in User-Generated Content

One frustrating aspect of CSS development is when user-generated content includes inline styles, as would occur with some WYSIWYG editors in CMSs. In the CSS cascade, inline styles will override regular styles, so any undesirable element styling that occurs through generated content will be difficult, if not impossible, to change using customary CSS rules. You can circumvent this problem using the !important declaration, because a CSS rule with !important in an author stylesheet will override inline CSS.

For Print Stylesheets

Although this wouldn’t be necessary in all cases, and might be discouraged in some cases for the same reasons mentioned earlier, you could add !important declarations to your print-only stylesheets to help override specific styles without having to repeat selector specificity.

For Uniquely-Designed Blog Posts

If you’ve dabbled in uniquely-designed blog posts (many designers take issue with using “art direction” for this technique, and rightly so), as showcased on Heart Directed, you’ll know that such an undertaking requires each separately-designed article to have its own stylesheet, or else you need to use inline styles. You can give an individual page its own styles using the code presented in this post on the Digging Into WordPress blog.

The !important declaration could come in handy in such an instance, allowing you to easily override the default styles in order to create a unique experience for a single blog post or page on your site, without having to worry about natural CSS specificity.

Conclusion

The !important declaration is best reserved for special needs and users who want to make web content more accessible by easily overriding default user agent or author stylesheets. So you should do your best to give your CSS proper forethought and avoid this declaration wherever possible. Even in many of the uses described above, the inclusion of !important is not always necessary.

Nonetheless, !important is valid CSS. You might inherit a project wherein the previous developers used it, or you might have to patch something up quickly — so it could come in handy. It’s certainly beneficial to understand it better and be prepared to use it should the need arise.

Do you ever use !important in your stylesheets? When do you do so? Are there any other circumstances you can think of that would require its use?