PostCSS High Contrast

PostCSS High Contrast is PostCSS plugin that helps automatically convert all colors to high contrast. This Plugin gives you ability to create high contrast version of your project with ease.

Why?

Accessible websites are getting more popular. Some countries even pass laws obliging IT companies create high contrast versions of their projects. Creating high contrast version of your project due some reasons can be painful.

Live Example

Basic Usage

postcss([
	require('postcss-high-contrast')({
		aggressiveHC: true,
		aggressiveHCDefaultSelectorList: ['h1', 'h2', 'h3', 'h4', 'h5', 'h6', 'p', 'li', 'th', 'td'],
		aggressiveHCCustomSelectorList: ['div', 'span'],

		colorProps: ['color', 'fill'],

		backgroundColor: '#000',
		altBgColor: '#fff',

		textColor: '#fff',

		buttonSelector: ['button'],
		buttonColor: '#000',
		buttonBackgroundColor: '#fcff3c',
		buttonBorderColor: 'none',
		
		linkSelectors:  ['a'],
		linkColor: '#fcff3c',
		linkHoverColor: '#fcff3c',

		borderColor: '#fff',
		disableShadow: true,
		
		customSelectors: ['input'],
		customSelectorColor: '#fff',
		customSelectorBackgroundColor: '#000',
		customSelectorBorderdColor: '#fff',
		
		selectorsBlackList: ['textfield'],

		imageFilter: 'invert(100%)',
		imageSelectors: ['img'],

		removeCSSProps: false,
        CSSPropsWhiteList: ['background', 'background-color', 'color', 'border', 'border-top', 'border-bottom',
            'border-left', 'border-right', 'border-color', 'border-top-color', 'border-right-color',
            'border-bottom-color', 'border-left-color', 'box-shadow', 'filter', 'text-shadow', 'fill']
	})
]);

How It works?

None Aggressive Mode

PostCSS High Contrast plugin will find all colors and replace them to high contrast ones. input.css:

body {
	background: #fff;
	color: #000;
}

a {
	color: #0b39e1;
}

output.css:

body {
	background: #000;
	color: #fff;
}

a {
	color: #fcff3c;
}

Aggressive Mode

In addition to replacing colors to high contrast colors, there is "Aggressive Mode". "Aggressive Mode" (aggressiveHC) is enabled by default. If selector doesn't have color property it will automatically append it for increasing specificity and providing more accurate results. input.css:

h1 {
	font-size: 48px;
	margin: 0;
	padding: 0 24px;
	width: 100%;
}

p {
	font-size: 48px;
	margin: 0 0 24px;
}

output.css:

h1 {
	color: #fff;
	font-size: 48px;
	margin: 0;
	padding: 0 24px;
	width: 100%;
}

p {
	color: #fff;
	font-size: 48px;
	margin: 0 0 24px;
}

Use aggressiveHCDefaultSelectorList and aggressiveHCCustomSelectorList to define own lists of properties.

Removing Unused CSS

For better css optimization there is an option to remove unused css. input.css:

h1 {
	font-size: 48px;
	margin: 0;
	padding: 0 24px;
	width: 100%;
}

p {
	font-size: 48px;
	margin: 0 0 24px;
}

output.css:

h1 {
	color: #fff;
}

p {
	color: #fff;
}

For merging CSS selectors use CSS minifiers like CSSNano or CSSO. If you are using PostCSS High Contrast Plugins with some other PostCSS Plugins like PostCSS Increase Text Sizes you might need some other properties to remain. For this case there is CSSPropsWhiteList option that prevents from deleting css properties:

CSSPropsWhiteList: ['background', 'background-color', 'color', 'border', 'border-top', 'border-bottom', 'border-left', 'border-right', 'border-color', 'border-top-color', 'border-right-color', 'border-bottom-color', 'border-left-color', 'box-shadow', 'filter', 'text-shadow']

WARNING!

removeCSSProps also can remove css properies generated by PostCSS High Contrast. To Prevent this use CSSPropsWhiteList!

Appending to wepbage

Using this plugin it's better to generate new high contrast version of css file. Than it is very easy to add/append high contrast version css to a webpage using JavaScript. JQuery example:

function appendHighContrastCss(){
	var hc = '<link rel="stylesheet" href="/assets/css/high-contrast.css" id="hccss"/>';

	if(!$('#highContrastCss').length ){
		$('head').append(hc);
	} else {
		$('#hccss').remove();
	}
}

$('a.high-contrast').click(loadHighContrastCSS);
	appendHighContrastCss();
}

Tip: use cookies to remember turned on high contrast css on different sessions and pages.

Options

Name	Default Value	Description
aggressiveHC	true	Will append properties even if they do not exist
aggressiveHCDefaultSelectorList	['h1', 'h2', 'h3', 'h4', 'h5', 'h6','p', 'li', 'th', 'td']	Default list of selectors for aggressive property append
aggressiveHCCustomSelectorList	['span']	Custom list of selectors for aggressive property append
colorProps	['color','fill']	List of Properties that will be considered for color changing
backgroundColor	#000	Backgound color
altBgColor	#fff	Alternative background color
textColor	#fff	Text color
buttonSelector	[button]	Button Selector
buttonColor	#000	Button color
buttonBackgroundColor	#fcff3c	Button background color
buttonBorderColor	none	Button border color
linkColor	#fcff3c	Link color
linkHoverBgColor	#fff	Link hover bacground color
linkHoverColor	#000	Link hover color
borderColor	#fff	Border color
disableShadow	true	Disable shadow
imageFilter	false/invert(100%)/grayscale(100%)/contrast(200%)	Image Filter (disabled by default). false to disable. Any css filter option can be passed
imageSelectors	['img']	Default list of image selectors to apply imageFilter
removeCSSProps	false	This option will remove all unused CSS selectors or properties for better optimization. Use CSS minifiers like CSSNano or CSSO to merge selectors
CSSPropsWhiteList	['background', 'background-color', 'color', 'border', 'border-top', 'border-bottom', 'border-left', 'border-right', 'border-color', 'border-top-color', 'border-right-color', 'border-bottom-color', 'border-left-color', 'box-shadow', 'filter', 'text-shadow']	CSS properties whitelist

Used by

Magyar Posta Signal IDUNA

Works great with:

PostCSS Increase Text Sizes