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diff --git a/css.html.markdown b/css.html.markdown index 7224d80a..8ee4f4b9 100644 --- a/css.html.markdown +++ b/css.html.markdown @@ -4,25 +4,22 @@ contributors: - ["Mohammad Valipour", "https://github.com/mvalipour"] - ["Marco Scannadinari", "https://github.com/marcoms"] - ["Geoffrey Liu", "https://github.com/g-liu"] + - ["Connor Shea", "https://github.com/connorshea"] + - ["Deepanshu Utkarsh", "https://github.com/duci9y"] + - ["Tyler Mumford", "https://tylermumford.com"] filename: learncss.css --- -In the early days of the web there were no visual elements, just pure text. But with the -further development of browsers, fully visual web pages also became common. -CSS is the standard language that exists to keep the separation between -the content (HTML) and the look-and-feel of web pages. +Web pages are built with HTML, which specifies the content of a page. CSS (Cascading Style Sheets) is a separate language which specifies a page's **appearance**. -In short, what CSS does is to provide a syntax that enables you to target -different elements on an HTML page and assign different visual properties to them. +CSS code is made of static *rules*. Each rule takes one or more *selectors* and gives specific *values* to a number of visual *properties*. Those properties are then applied to the page elements indicated by the selectors. -Like any other languages, CSS has many versions. Here we focus on CSS2.0, -which is not the most recent version, but is the most widely supported and compatible version. +This guide has been written with CSS 2 in mind, which is extended by the new features of CSS 3. -**NOTE:** Because the outcome of CSS consists of visual effects, in order to -learn it, you need try everything in a -CSS playground like [dabblet](http://dabblet.com/). +**NOTE:** Because CSS produces visual results, in order to learn it, you need to try everything in a CSS playground like [dabblet](http://dabblet.com/). The main focus of this article is on the syntax and some general tips. +## Syntax ```css /* comments appear inside slash-asterisk, just like this line! @@ -32,92 +29,103 @@ The main focus of this article is on the syntax and some general tips. ## SELECTORS #################### */ -/* Generally, the primary statement in CSS is very simple */ +/* the selector is used to target an element on a page. */ selector { property: value; /* more properties...*/ } -/* the selector is used to target an element on page. - -You can target all elements on the page using asterisk! */ -* { color:red; } - /* -Given an element like this on the page: +Here is an example element: -<div class='some-class class2' id='someId' attr='value' otherAttr='en-us foo bar' /> +<div class='class1 class2' id='anID' attr='value' otherAttr='en-us foo bar' /> */ -/* you can target it by its name */ -.some-class { } +/* You can target it using one of its CSS classes */ +.class1 { } -/* or by both classes! */ -.some-class.class2 { } +/* or both classes! */ +.class1.class2 { } -/* or by its element name */ +/* or its name */ div { } /* or its id */ -#someId { } +#anID { } -/* or by the fact that it has an attribute! */ +/* or using the fact that it has an attribute! */ [attr] { font-size:smaller; } /* or that the attribute has a specific value */ [attr='value'] { font-size:smaller; } -/* start with a value (CSS3) */ +/* starts with a value (CSS 3) */ [attr^='val'] { font-size:smaller; } -/* or ends with (CSS3) */ +/* or ends with a value (CSS 3) */ [attr$='ue'] { font-size:smaller; } -/* or select by one of the values from the whitespace separated list (CSS3) */ -[otherAttr~='foo'] { font-size:smaller; } +/* or contains a value in a space-separated list */ +[otherAttr~='foo'] { } +[otherAttr~='bar'] { } -/* or value can be exactly “value” or can begin with “value” immediately followed by “-” (U+002D) */ +/* or contains a value in a dash-separated list, ie, "-" (U+002D) */ [otherAttr|='en'] { font-size:smaller; } -/* and more importantly you can combine these together -- there shouldn't be -any space between different parts because that makes it to have another -meaning. */ +/* You can combine different selectors to create a more focused selector. Don't + put spaces between them. */ div.some-class[attr$='ue'] { } -/* you can also select an element based on its parent. */ +/* You can select an element which is a child of another element */ +div.some-parent > .class-name { } + +/* or a descendant of another element. Children are the direct descendants of + their parent element, only one level down the tree. Descendants can be any + level down the tree. */ +div.some-parent .class-name { } + +/* Warning: the same selector without a space has another meaning. + Can you guess what? */ +div.some-parent.class-name { } -/* an element which is direct child of an element (selected the same way) */ -div.some-parent > .class-name {} +/* You may also select an element based on its adjacent sibling */ +.i-am-just-before + .this-element { } -/* or any of its parents in the tree - the following basically means any element that has class "class-name" - and is child of a div with class name "some-parent" IN ANY DEPTH */ -div.some-parent .class-name {} +/* or any sibling preceding it */ +.i-am-any-element-before ~ .this-element { } -/* warning: the same selector without space has another meaning. - can you say what? */ -div.some-parent.class-name {} +/* There are some selectors called pseudo classes that can be used to select an + element only when it is in a particular state */ -/* you also might choose to select an element based on its direct - previous sibling */ -.i-am-before + .this-element { } +/* for example, when the cursor hovers over an element */ +selector:hover { } -/* or any sibling before this */ -.i-am-any-before ~ .this-element {} +/* or a link has been visited */ +selector:visited { } -/* There are some pseudo classes that allows you to select an element - based on its page behaviour (rather than page structure) */ +/* or hasn't been visited */ +selected:link { } -/* for example for when an element is hovered */ -selector:hover {} +/* or an element is in focus */ +selected:focus { } -/* or a visited link */ -selected:visited {} +/* any element that is the first child of its parent */ +selector:first-child {} -/* or not visited link */ -selected:link {} +/* any element that is the last child of its parent */ +selector:last-child {} -/* or an input element which is focused */ -selected:focus {} +/* Just like pseudo classes, pseudo elements allow you to style certain parts of a document */ +/* matches a virtual first child of the selected element */ +selector::before {} + +/* matches a virtual last child of the selected element */ +selector::after {} + +/* At appropriate places, an asterisk may be used as a wildcard to select every + element */ +* { } /* all elements */ +.parent * { } /* all descendants */ +.parent > * { } /* all children */ /* #################### ## PROPERTIES @@ -125,123 +133,122 @@ selected:focus {} selector { - /* Units */ - width: 50%; /* in percent */ - font-size: 2em; /* times current font-size */ - width: 200px; /* in pixels */ - font-size: 20pt; /* in points */ - width: 5cm; /* in centimeters */ - min-width: 50mm; /* in millimeters */ - max-width: 5in; /* in inches. max-(width|height) */ - height: 0.2vh; /* times vertical height of browser viewport (CSS3) */ - width: 0.4vw; /* times horizontal width of browser viewport (CSS3) */ - min-height: 0.1vmin; /* the lesser of vertical, horizontal dimensions of browser viewport (CSS3) */ - max-width: 0.3vmax; /* same as above, except the greater of the dimensions (CSS3) */ + /* Units of length can be absolute or relative. */ + + /* Relative units */ + width: 50%; /* percentage of parent element width */ + font-size: 2em; /* multiples of element's original font-size */ + font-size: 2rem; /* or the root element's font-size */ + font-size: 2vw; /* multiples of 1% of the viewport's width (CSS 3) */ + font-size: 2vh; /* or its height */ + font-size: 2vmin; /* whichever of a vh or a vw is smaller */ + font-size: 2vmax; /* or greater */ + + /* Absolute units */ + width: 200px; /* pixels */ + font-size: 20pt; /* points */ + width: 5cm; /* centimeters */ + min-width: 50mm; /* millimeters */ + max-width: 5in; /* inches */ /* Colors */ - background-color: #F6E; /* in short hex */ - background-color: #F262E2; /* in long hex format */ - background-color: tomato; /* can be a named color */ - background-color: rgb(255, 255, 255); /* in rgb */ - background-color: rgb(10%, 20%, 50%); /* in rgb percent */ - background-color: rgba(255, 0, 0, 0.3); /* in semi-transparent rgb (CSS3) */ - background-color: transparent; /* see thru */ - background-color: hsl(0, 100%, 50%); /* hsl format (CSS3). */ - background-color: hsla(0, 100%, 50%, 0.3); /* Similar to RGBA, specify opacity at end (CSS3) */ - + color: #F6E; /* short hex format */ + color: #FF66EE; /* long hex format */ + color: tomato; /* a named color */ + color: rgb(255, 255, 255); /* as rgb values */ + color: rgb(10%, 20%, 50%); /* as rgb percentages */ + color: rgba(255, 0, 0, 0.3); /* as rgba values (CSS 3) Note: 0 <= a <= 1 */ + color: transparent; /* equivalent to setting the alpha to 0 */ + color: hsl(0, 100%, 50%); /* as hsl percentages (CSS 3) */ + color: hsla(0, 100%, 50%, 0.3); /* as hsl percentages with alpha */ - /* Images */ - background-image: url(/path-to-image/image.jpg); /* quotes inside url() optional */ + /* Images as backgrounds of elements */ + background-image: url(/img-path/img.jpg); /* quotes inside url() optional */ /* Fonts */ font-family: Arial; - font-family: "Courier New"; /* if name has space it appears in single or double quotes */ - font-family: "Courier New", Trebuchet, Arial, sans-serif; /* if first one was not found - browser uses the second font, and so forth */ + /* if the font family name has a space, it must be quoted */ + font-family: "Courier New"; + /* if the first one is not found, the browser uses the next, and so on */ + font-family: "Courier New", Trebuchet, Arial, sans-serif; } - ``` ## Usage -Save any CSS you want in a file with extension `.css`. +Save a CSS stylesheet with the extension `.css`. ```xml -<!-- you need to include the css file in your page's <head>: --> +<!-- You need to include the css file in your page's <head>. This is the + recommended method. Refer to http://stackoverflow.com/questions/8284365 --> <link rel='stylesheet' type='text/css' href='path/to/style.css' /> -<!-- you can also include some CSS inline in your markup. However it is highly -recommended to avoid this. --> +<!-- You can also include some CSS inline in your markup. --> <style> a { color: purple; } </style> -<!-- or directly set CSS properties on the element. -This has to be avoided as much as you can. --> +<!-- Or directly set CSS properties on the element. --> <div style="border: 1px solid red;"> </div> - ``` -## Precedence +## Precedence or Cascade + +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. Rules with a more specific selector take precedence over a less specific one, and a rule occuring later in the stylesheet overwrites a previous one. -As you noticed an element may be targetted by more than one selector. -and may have a property set on it in more than one. -In these cases, one of the rules takes precedence over others. +This process is called cascading, hence the name Cascading Style Sheets. Given the following CSS: ```css -/*A*/ +/* A */ p.class1[attr='value'] -/*B*/ -p.class1 {} +/* B */ +p.class1 { } -/*C*/ -p.class2 {} +/* C */ +p.class2 { } -/*D*/ -p {} +/* D */ +p { } -/*E*/ +/* E */ p { property: value !important; } - ``` and the following markup: ```xml -<p style='/*F*/ property:value;' class='class1 class2' attr='value'> -</p> +<p style='/*F*/ property:value;' class='class1 class2' attr='value' /> ``` -The precedence of style is as followed: -Remember, the precedence is for each **property**, not for the entire block. +The precedence of style is as follows. Remember, the precedence is for each **property**, not for the entire block. -* `E` has the highest precedence because of the keyword `!important`. - It is recommended to avoid this unless it is strictly necessary to use. -* `F` is next, because it is inline style. -* `A` is next, because it is more "specific" than anything else. - more specific = more specifiers. here 3 specifiers: 1 tagname `p` + - class name `class1` + 1 attribute `attr='value'` -* `C` is next. although it has the same specificness as `B` - but it appears last. -* Then is `B` -* and lastly is `D`. +* `E` has the highest precedence because of the keyword `!important`. It is recommended that you avoid its usage. +* `F` is next, because it is an inline style. +* `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'`. +* `C` is next, even though it has the same specificity as `B`. This is because it appears after `B`. +* `B` is next. +* `D` is the last one. ## Compatibility -Most of the features in CSS2 (and gradually in CSS3) are compatible across -all browsers and devices. But it's always vital to have in mind the compatibility -of what you use in CSS with your target browsers. +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. -[QuirksMode CSS](http://www.quirksmode.org/css/) is one of the best sources for this. +## Resources -To run a quick compatibility check, [CanIUse](http://caniuse.com) is a great resource. +* [CanIUse](http://caniuse.com) (Detailed compatibility info) +* [Dabblet](http://dabblet.com/) (CSS playground) +* [Mozilla Developer Network's CSS documentation](https://developer.mozilla.org/en-US/docs/Web/CSS) (Tutorials and reference) +* [Codrops' CSS Reference](http://tympanus.net/codrops/css_reference/) (Reference) ## Further Reading * [Understanding Style Precedence in CSS: Specificity, Inheritance, and the Cascade](http://www.vanseodesign.com/css/css-specificity-inheritance-cascaade/) +* [Selecting elements using attributes](https://css-tricks.com/almanac/selectors/a/attribute/) * [QuirksMode CSS](http://www.quirksmode.org/css/) * [Z-Index - The stacking context](https://developer.mozilla.org/en-US/docs/Web/Guide/CSS/Understanding_z_index/The_stacking_context) +* [SASS](http://sass-lang.com/) and [LESS](http://lesscss.org/) for CSS pre-processing +* [CSS-Tricks](https://css-tricks.com) |