CSS hack
A CSS hack is a coding technique used to hide or show CSS markup depending on the browser, version number, or capabilities. Browsers have different interpretations of CSS behavior and different levels of support for the W3C standards. CSS hacks are sometimes used to achieve consistent layout appearance in multiple browsers that do not have compatible rendering. Most of these hacks do not work in modern versions of the browsers, and other techniques, such as feature support detection, have become more prevalent.
Types of hacks
Invalid or non-compliant CSS
Due to quirks in the interpretation of CSS by various browsers, most CSS hacks involve writing invalid CSS rules that are interpreted only by specific browsers, or relying on bugs in specific browsers. An example of this is prefixing rules with an underscore (as in _width
) to target Internet Explorer 6—other browsers will ignore the line, allowing it to be used to write code specific to one browser.
Conditional comments
Prior to version 10, Internet Explorer supported a special comment syntax that would allow blocks of HTML to be read only by specific versions of the browser. These comments are mostly used to provide specific CSS and JavaScript workarounds to older versions of the browser. No other browsers interpreted these comments or offered similar functionality.
The following are examples of the different syntax for these comments.
<head>
<title>Test</title>
<link href="all_browsers.css" rel="stylesheet" type="text/css">
<!--[if IE]> <link href="ie_only.css" rel="stylesheet" type="text/css"> <![endif]-->
<!--[if lt IE 7]> <link href="ie_6_and_below.css" rel="stylesheet" type="text/css"> <![endif]-->
<!--[if !lt IE 7]> <![IGNORE[--><![IGNORE[]]> <link href="recent.css" rel="stylesheet" type="text/css"> <!--<![endif]-->
<!--[if !IE]--> <link href="not_ie.css" rel="stylesheet" type="text/css"> <!--<![endif]-->
</head>
Criticism
Hiding code using hacks often leads to pages being incorrectly displayed when browsers are updated. These hacks can lead to unexpected behavior in newer browsers that may interpret them differently than their predecessors. Since Internet Explorer 6 and 7 have fallen out of use, CSS hacks have declined as well. Modern methods of feature targeting are less fragile and error-prone.
Alternatives
Browser prefixes
Each of the most popular browser rendering engines has its own vendor-specific prefix for experimental properties. However, due to the proliferation of these properties in live code, the browser vendors have begun to move away from this in favor of user-controlled feature flags.[1]
List of prefixes
The following is a list of prefixes from various layout engines:
Vendor Prefix | In Use | Layout Engine | Created by | Used by |
---|---|---|---|---|
-ah- |
yes | Formatter | Antenna House | Antenna House Formatter |
-apple- |
yes | WebKit | Apple Inc. | Apple Safari 2.0, Opera Widgets, WebKit-Based Browsers (as legacy prefix) |
-atsc- |
Advanced Television Systems Committee standards | |||
-epub- |
yes | WebKit | EPUB Working Group | Chromium / Google Chrome, WebKit-Based Browsers |
-hp- |
Hewlett-Packard (now HP Inc.) | |||
-khtml- |
yes / yes | KHTML / WebKit | KDE | KDE Konqueror / Apple Safari 1.1 through Safari 2.0, WebKit-Based Browsers (as a legacy prefix) |
-moz- |
yes | Gecko | Mozilla Foundation | Gecko-Based Browsers[?], Mozilla Firefox |
-ms- |
yes | Trident / MSHTML | Microsoft Corporation | Microsoft Internet Explorer |
mso- |
Office | Microsoft Corporation | Microsoft Office[?] | |
-o- |
yes | Presto | Opera Software | Opera desktop Browser up to version 12.16, Opera Mini, and Opera Mobile up to version 12.1, Nintendo DS & Nintendo DSi Browser, Nintendo Wii Internet Channel |
prince- |
yes | Prince | YesLogic | YesLogic Prince |
-rim- |
WebKit | BlackBerry Limited | RIM Blackberry Browser | |
-ro- |
yes | MARTHA | Real Objects | Real Objects PDFreactor |
-tc- |
TallComponents | TallComponents | ||
-wap- |
yes | Presto | The WAP Forum | Opera Desktop Browser and Opera Mobile, The WAP Forum |
-webkit- |
yes | WebKit/Blink | Apple Inc. (WebKit)/Google Inc. (Blink) | Apple Safari & Safari for iOS (WebKit), Chromium / Google Chrome desktop and mobile (Blink), Opera desktop and mobile from version 14 (Blink), Android browser (Blink), Nokia MeeGo Browser 8.5, Nokia Symbian Browser 7.0 and later (WebKit), Blackberry Browser 6.0 and later (WebKit). |
-xv- |
no | Presto | Opera Software | Opera Desktop Browser for Windows 2000/XP |
Example
/* Cross-browser css3 linear-gradient */
.linear-gradient {
/* Gecko browser (Firefox) */
background-image: -moz-linear-gradient(top, #D7D 0%, #068 100%);
/* Opera */
background-image: -o-linear-gradient(top, #D7D 0%, #068 100%);
/* older Webkit syntax */
background-image: -webkit-gradient(linear, left top, left bottom,
color-stop(0, #D7D), color-stop(1, #068));
/* Webkit (Safari, Chrome, iOS, Android) */
background-image: -webkit-linear-gradient(top, #D7D 0%, #068 100%);
/* W3C */
background-image: linear-gradient(to bottom, #D7D 0%, #068 100%);
}
Limitations
Vendor prefixes were designed for features that were under development, meaning that the syntax may not even be final. Also, adding a rule for each browser's implementation of a function does not scale well when you want to support many browsers. Consequently, the major browser vendors are moving away from vendor prefixes in favor of other methods such as @supports
feature queries.
Feature detection
JavaScript feature detection
Multiple JavaScript such as Modernizr add classes to the html
element, allowing for CSS rules such as .cssgradients .header
.
@supports
A new feature known as feature queries was introduced in CSS 3, allowing the detection of specific functionality within the CSS (without requiring the use of a JavaScript library for feature detection). This new directive can be used to check for the support or lack of support for a specific feature, and checks can be combined with and
, or
, and not
. Obviously, @supports
rules will only work on browsers that support @supports
.
header {
display: block;
}
@supports (display:flexbox) {
header {
display: flexbox;
}
}
JavaScript polyfills
While JavaScript feature detection and @supports
rules can help to target browsers that require fallback functionality, they will not address bugs in specific browsers or enable that advanced functionality. Polyfills, scripts that make behavior consistent across all browsers, can be used to add support for new CSS rules (for example, media queries in IE 8) as well as fix bugs in specific browsers (for example, fixing the implementation of viewport units in mobile Safari). Since polyfills add or fix functionality in browsers that don't have it, they serve a different purpose than feature queries, but can be used in combination with them.
See also
Notes
- ^ "Vendor Prefix". Mozilla Developer Network. Retrieved 12 October 2016.
External links
- Browser Strangeness - Jeff Clayton's Live CSS hacks and tests to filter for mainstream browsers, including the only known CSS Hacks for Safari 7 and 8
- browserhacks.com - Multiple browser filter methods and tests (Hugo Giraudel, Joshua Hibbert, Tim Pietrusky, Fabrice Weinberg, Jeff Clayton)
- Safari/Webkit (webkit) prefix filters refix filters]
- Mozilla (moz) prefix filters
- Opera (wap) prefix filters - This page has all of Opera's CSS selectors.
- CSS Filters – A fairly complete table of CSS hacks which show and hide rules from specific browsers.
- [ CSS Filters – CSS-only Filters Summary] – More CSS filters.
- Filters and Cross-Over – CSS filters. Parsing errors marked red.
- - CSS Browser Selector - Allows to combine browser specific CSS in single stylesheet (using JavaScript).
- - #IEroot - Targeting IE with a single stylesheet containing all CSS (without using JavaScript, but using conditional comments to assign browser-specific tag to arbitrary content root [div])