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[css/en] Fixed grammar, increased clarity.
Also fixed extraneous whitespace, code mistakes, made sure line width was <80 characters.
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duci9y
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@ -5,26 +5,21 @@ contributors:
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- ["Marco Scannadinari", "https://github.com/marcoms"]
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- ["Geoffrey Liu", "https://github.com/g-liu"]
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- ["Connor Shea", "https://github.com/connorshea"]
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- ["Deepanshu Utkarsh", "https://github.com/duci9y"]
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filename: learncss.css
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---
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In the early days of the web there were no visual elements, just pure text. But with the
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further development of browsers, fully visual web pages also became common.
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CSS is the standard language that exists to keep the separation between
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the content (HTML) and the look-and-feel of web pages.
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In the early days of the web there were no visual elements, just pure text. But with further development of web browsers, fully visual web pages also became common.
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In short, what CSS does is to provide a syntax that enables you to target
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different elements on an HTML page and assign different visual properties to them.
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CSS helps maintain separation between the content (HTML) and the look-and-feel of a web page.
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Like any other languages, CSS has many versions. Here we focus on CSS2.0,
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which is not the most recent version, but is the most widely supported and compatible version.
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CSS lets you target different elements on an HTML page and assign different visual properties to them.
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**NOTE:** Because the outcome of CSS consists of visual effects, in order to
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learn it, you need try everything in a
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CSS playground like [dabblet](http://dabblet.com/).
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This guide has been written for CSS 2, though CSS 3 is fast becoming popular.
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**NOTE:** Because CSS produces visual results, in order to learn it, you need try everything in a CSS playground like [dabblet](http://dabblet.com/).
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The main focus of this article is on the syntax and some general tips.
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```css
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/* comments appear inside slash-asterisk, just like this line!
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there are no "one-line comments"; this is the only comment style */
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@ -33,92 +28,89 @@ The main focus of this article is on the syntax and some general tips.
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## SELECTORS
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#################### */
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/* Generally, the primary statement in CSS is very simple */
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/* the selector is used to target an element on a page.
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selector { property: value; /* more properties...*/ }
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/* the selector is used to target an element on page.
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You can target all elements on the page using asterisk! */
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* { color:red; }
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/*
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Given an element like this on the page:
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Here is an example element:
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<div class='some-class class2' id='someId' attr='value' otherAttr='en-us foo bar' />
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<div class='class1 class2' id='anID' attr='value' otherAttr='en-us foo bar' />
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*/
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/* you can target it by its name */
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.some-class { }
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/* You can target it using one of its CSS classes */
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.class1 { }
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/* or by both classes! */
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.some-class.class2 { }
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/* or both classes! */
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.class1.class2 { }
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/* or by its element name */
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/* or its name */
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div { }
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/* or its id */
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#someId { }
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#anID { }
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/* or by the fact that it has an attribute! */
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/* or using the fact that it has an attribute! */
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[attr] { font-size:smaller; }
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/* or that the attribute has a specific value */
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[attr='value'] { font-size:smaller; }
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/* start with a value (CSS3) */
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/* starts with a value (CSS 3) */
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[attr^='val'] { font-size:smaller; }
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/* or ends with (CSS3) */
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/* or ends with a value (CSS 3) */
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[attr$='ue'] { font-size:smaller; }
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/* or select by one of the values from the whitespace separated list (CSS3) */
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[otherAttr~='foo'] { font-size:smaller; }
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/* or contains a value in a space-separated list */
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[otherAttr~='foo'] { }
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[otherAttr~='bar'] { }
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/* or value can be exactly “value” or can begin with “value” immediately followed by “-” (U+002D) */
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/* or contains a value in a dash-separated list, ie, "-" (U+002D) */
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[otherAttr|='en'] { font-size:smaller; }
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/* and more importantly you can combine these together -- there shouldn't be
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any space between different parts because that makes it to have another
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meaning. */
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/* You can concatenate different selectors to create a narrower selector. Don't
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put spaces between them. */
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div.some-class[attr$='ue'] { }
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/* you can also select an element based on its parent. */
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/* You can select an element which is a child of another element */
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div.some-parent > .class-name { }
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/* an element which is direct child of an element (selected the same way) */
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div.some-parent > .class-name {}
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/* or a descendant of another element. Children are the direct descendants of
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their parent element, only one level down the tree. Descendants can be any
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level down the tree. */
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div.some-parent .class-name { }
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/* or any of its parents in the tree
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the following basically means any element that has class "class-name"
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and is child of a div with class name "some-parent" IN ANY DEPTH */
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div.some-parent .class-name {}
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/* Warning: the same selector without a space has another meaning.
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Can you guess what? */
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div.some-parent.class-name { }
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/* warning: the same selector without space has another meaning.
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can you say what? */
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div.some-parent.class-name {}
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/* You may also select an element based on its adjacent sibling */
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.i-am-just-before + .this-element { }
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/* you also might choose to select an element based on its direct
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previous sibling */
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.i-am-before + .this-element { }
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/* or any sibling preceding it */
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.i-am-any-element-before ~ .this-element { }
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/* or any sibling before this */
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.i-am-any-before ~ .this-element {}
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/* There are some selectors called pseudo classes that can be used to select an
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element when it is in a particular state */
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/* There are some pseudo classes that allows you to select an element
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based on its page behaviour (rather than page structure) */
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/* for example, when the cursor hovers over an element */
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selector:hover { }
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/* for example for when an element is hovered */
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selector:hover {}
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/* or a link has been visited */
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selector:visited { }
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/* or a visited link */
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selected:visited {}
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/* or hasn't been visited */
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selected:link { }
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/* or not visited link */
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selected:link {}
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/* or an input element which is focused */
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selected:focus {}
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/* or an element in focus */
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selected:focus { }
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/* At appropriate places, an asterisk may be used as a wildcard to select every
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element */
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* { } /* all elements */
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.parent * { } /* all descendants */
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.parent > * { } /* all children */
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/* ####################
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## PROPERTIES
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@ -126,126 +118,122 @@ selected:focus {}
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selector {
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/* Units */
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width: 50%; /* in percent */
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font-size: 2em; /* times current font-size */
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width: 200px; /* in pixels */
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font-size: 20pt; /* in points */
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width: 5cm; /* in centimeters */
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min-width: 50mm; /* in millimeters */
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max-width: 5in; /* in inches. max-(width|height) */
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height: 0.2vh; /* times vertical height of browser viewport (CSS3) */
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width: 0.4vw; /* times horizontal width of browser viewport (CSS3) */
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min-height: 0.1vmin; /* the lesser of vertical, horizontal dimensions of browser viewport (CSS3) */
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max-width: 0.3vmax; /* same as above, except the greater of the dimensions (CSS3) */
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/* Units of length can be absolute or relative. */
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/* Relative units */
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width: 50%; /* percentage of parent element width */
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font-size: 2em; /* multiples of element's original font-size */
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font-size: 2rem; /* or the root element's font-size */
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font-size: 2vw; /* multiples of 1% of the viewport's width (CSS 3) */
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font-size: 2vh; /* or its height */
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font-size: 2vmin; /* whichever of a vh or a vw is smaller */
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font-size: 2vmax; /* or greater */
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/* Absolute units */
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width: 200px; /* pixels */
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font-size: 20pt; /* points */
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width: 5cm; /* centimeters */
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min-width: 50mm; /* millimeters */
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max-width: 5in; /* inches */
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/* Colors */
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background-color: #F6E; /* in short hex */
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background-color: #F262E2; /* in long hex format */
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background-color: tomato; /* can be a named color */
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background-color: rgb(255, 255, 255); /* in rgb */
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background-color: rgb(10%, 20%, 50%); /* in rgb percent */
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background-color: rgba(255, 0, 0, 0.3); /* in semi-transparent rgb (CSS3) */
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background-color: transparent; /* see thru */
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background-color: hsl(0, 100%, 50%); /* hsl format (CSS3). */
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background-color: hsla(0, 100%, 50%, 0.3); /* Similar to RGBA, specify opacity at end (CSS3) */
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color: #F6E; /* short hex format */
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color: #FF66EE; /* long hex format */
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color: tomato; /* a named color */
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color: rgb(255, 255, 255); /* as rgb values */
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color: rgb(10%, 20%, 50%); /* as rgb percentages */
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color: rgba(255, 0, 0, 0.3); /* as rgba values (CSS 3) Note: 0 < a < 1 */
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color: transparent; /* equivalent to setting the alpha to 0 */
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color: hsl(0, 100%, 50%); /* as hsl percentages (CSS 3) */
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color: hsla(0, 100%, 50%, 0.3); /* as hsla percentages with alpha */
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/* Images */
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background-image: url(/path-to-image/image.jpg); /* quotes inside url() optional */
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/* Images as backgrounds of elements */
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background-image: url(/img-path/img.jpg); /* quotes inside url() optional */
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/* Fonts */
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font-family: Arial;
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font-family: "Courier New"; /* if name has space it appears in single or double quotes */
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font-family: "Courier New", Trebuchet, Arial, sans-serif; /* if first one was not found
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browser uses the second font, and so forth */
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/* if the font family name has a space, it must be quoted */
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font-family: "Courier New";
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/* if the first one is not found, the browser uses the next, and so on */
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font-family: "Courier New", Trebuchet, Arial, sans-serif;
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}
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```
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## Usage
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Save any CSS you want in a file with extension `.css`.
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Save a CSS stylesheet with the extension `.css`.
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```xml
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<!-- you need to include the css file in your page's <head>: -->
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<!-- You need to include the css file in your page's <head>. This is the
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recommended method. Refer to http://stackoverflow.com/questions/8284365 -->
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<link rel='stylesheet' type='text/css' href='path/to/style.css' />
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<!-- you can also include some CSS inline in your markup. However it is highly
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recommended to avoid this. -->
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<!-- You can also include some CSS inline in your markup. -->
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<style>
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a { color: purple; }
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</style>
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<!-- or directly set CSS properties on the element.
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This has to be avoided as much as you can. -->
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<!-- Or directly set CSS properties on the element. -->
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<div style="border: 1px solid red;">
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</div>
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```
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## Precedence
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## Precedence or Cascade
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As you noticed an element may be targetted by more than one selector.
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and may have a property set on it in more than one.
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In these cases, one of the rules takes precedence over others.
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An element may be targeted by multiple selectors and may have a property set on it in more than once. In these cases, one of the rules takes precedence over others. Generally, a rule in a more specific selector take precedence over a less specific one, and a rule occuring later in the stylesheet overwrites a previous one.
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This process is called cascading, hence the name Cascading Style Sheets.
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Given the following CSS:
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```css
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/*A*/
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/* A */
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p.class1[attr='value']
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/*B*/
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p.class1 {}
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/* B */
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p.class1 { }
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/*C*/
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p.class2 {}
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/* C */
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p.class2 { }
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/*D*/
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p {}
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/* D */
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p { }
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/*E*/
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/* E */
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p { property: value !important; }
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```
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and the following markup:
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```xml
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<p style='/*F*/ property:value;' class='class1 class2' attr='value'>
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</p>
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<p style='/*F*/ property:value;' class='class1 class2' attr='value' />
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```
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The precedence of style is as followed:
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Remember, the precedence is for each **property**, not for the entire block.
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The precedence of style is as follows. Remember, the precedence is for each **property**, not for the entire block.
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* `E` has the highest precedence because of the keyword `!important`.
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It is recommended to avoid this unless it is strictly necessary to use.
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* `F` is next, because it is inline style.
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* `A` is next, because it is more "specific" than anything else.
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more specific = more specifiers. here 3 specifiers: 1 tagname `p` +
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class name `class1` + 1 attribute `attr='value'`
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* `C` is next. although it has the same specificness as `B`
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but it appears last.
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* Then is `B`
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* and lastly is `D`.
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* `E` has the highest precedence because of the keyword `!important`. It is recommended that you avoid its usage.
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* `F` is next, because it is an inline style.
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* `A` is next, because it is more "specific" than anything else. It has 3 specifiers: The name of the element `p`, its class `class1`, an attribute `attr='value'`.
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* `C` is next, even though it has the same specificity as `B`. This is because it appears after `B`.
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* `B` is next.
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* `D` is the last one.
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## Compatibility
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Most of the features in CSS2 (and gradually in CSS3) are compatible across
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all browsers and devices. But it's always vital to have in mind the compatibility
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of what you use in CSS with your target browsers.
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Most of the features in CSS 2 (and many in CSS 3) are available across all browsers and devices. But it's always good practice to check before using a new feature.
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[QuirksMode CSS](http://www.quirksmode.org/css/) is one of the best sources for this.
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## Resources
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To run a quick compatibility check, [Can I Use...](http://caniuse.com) is a great resource.
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* To run a quick compatibility check, [CanIUse](http://caniuse.com).
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* CSS Playground [Dabblet](http://dabblet.com/).
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* [Mozilla Developer Network's CSS documentation](https://developer.mozilla.org/en-US/docs/Web/CSS)
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* [Codrops' CSS Reference](http://tympanus.net/codrops/css_reference/)
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## Further Reading
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* [Mozilla Developer Network's CSS documentation](https://developer.mozilla.org/en-US/docs/Web/CSS)
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* [Codrops' CSS Reference](http://tympanus.net/codrops/css_reference/)
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* [Understanding Style Precedence in CSS: Specificity, Inheritance, and the Cascade](http://www.vanseodesign.com/css/css-specificity-inheritance-cascaade/)
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* [Selecting elements using attributes](https://css-tricks.com/almanac/selectors/a/attribute/)
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* [QuirksMode CSS](http://www.quirksmode.org/css/)
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* [Z-Index - The stacking context](https://developer.mozilla.org/en-US/docs/Web/Guide/CSS/Understanding_z_index/The_stacking_context)
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* [SCSS](http://sass-lang.com/) and [LESS](http://lesscss.org/) for CSS pre-processing
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* [SASS](http://sass-lang.com/) and [LESS](http://lesscss.org/) for CSS pre-processing
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* [CSS-Tricks](https://css-tricks.com)
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