mirror of
https://github.com/adambard/learnxinyminutes-docs.git
synced 2024-12-26 00:31:39 +03:00
254 lines
8.3 KiB
Markdown
254 lines
8.3 KiB
Markdown
---
|
|
language: css
|
|
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"]
|
|
filename: learncss.css
|
|
---
|
|
|
|
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.
|
|
|
|
CSS helps maintain separation between the content (HTML) and the look-and-feel of a web page.
|
|
|
|
CSS lets you target different elements on an HTML page and assign different visual properties to them.
|
|
|
|
This guide has been written for CSS 2, though CSS 3 is fast becoming popular.
|
|
|
|
**NOTE:** Because CSS produces visual results, in order to learn it, you need 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.
|
|
|
|
```css
|
|
/* comments appear inside slash-asterisk, just like this line!
|
|
there are no "one-line comments"; this is the only comment style */
|
|
|
|
/* ####################
|
|
## SELECTORS
|
|
#################### */
|
|
|
|
/* the selector is used to target an element on a page.
|
|
selector { property: value; /* more properties...*/ }
|
|
|
|
/*
|
|
Here is an example element:
|
|
|
|
<div class='class1 class2' id='anID' attr='value' otherAttr='en-us foo bar' />
|
|
*/
|
|
|
|
/* You can target it using one of its CSS classes */
|
|
.class1 { }
|
|
|
|
/* or both classes! */
|
|
.class1.class2 { }
|
|
|
|
/* or its name */
|
|
div { }
|
|
|
|
/* or its id */
|
|
#anID { }
|
|
|
|
/* 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; }
|
|
|
|
/* starts with a value (CSS 3) */
|
|
[attr^='val'] { font-size:smaller; }
|
|
|
|
/* or ends with a value (CSS 3) */
|
|
[attr$='ue'] { font-size:smaller; }
|
|
|
|
/* or contains a value in a space-separated list */
|
|
[otherAttr~='foo'] { }
|
|
[otherAttr~='bar'] { }
|
|
|
|
/* or contains a value in a dash-separated list, ie, "-" (U+002D) */
|
|
[otherAttr|='en'] { font-size:smaller; }
|
|
|
|
|
|
/* You can concatenate different selectors to create a narrower selector. Don't
|
|
put spaces between them. */
|
|
div.some-class[attr$='ue'] { }
|
|
|
|
/* 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 { }
|
|
|
|
/* You may also select an element based on its adjacent sibling */
|
|
.i-am-just-before + .this-element { }
|
|
|
|
/* or any sibling preceding it */
|
|
.i-am-any-element-before ~ .this-element { }
|
|
|
|
/* There are some selectors called pseudo classes that can be used to select an
|
|
element when it is in a particular state */
|
|
|
|
/* for example, when the cursor hovers over an element */
|
|
selector:hover { }
|
|
|
|
/* or a link has been visited */
|
|
selector:visited { }
|
|
|
|
/* or hasn't been visited */
|
|
selected:link { }
|
|
|
|
/* or an element in focus */
|
|
selected:focus { }
|
|
|
|
/* any element that is the first child of its parent */
|
|
selector:first-child {}
|
|
|
|
/* any element that is the last child of its parent */
|
|
selector:last-child {}
|
|
|
|
/* 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
|
|
#################### */
|
|
|
|
selector {
|
|
|
|
/* 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 */
|
|
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 hsla percentages with alpha */
|
|
|
|
/* Images as backgrounds of elements */
|
|
background-image: url(/img-path/img.jpg); /* quotes inside url() optional */
|
|
|
|
/* Fonts */
|
|
font-family: Arial;
|
|
/* 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 a CSS stylesheet with the extension `.css`.
|
|
|
|
```xml
|
|
<!-- 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. -->
|
|
<style>
|
|
a { color: purple; }
|
|
</style>
|
|
|
|
<!-- Or directly set CSS properties on the element. -->
|
|
<div style="border: 1px solid red;">
|
|
</div>
|
|
```
|
|
|
|
## 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. 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.
|
|
|
|
This process is called cascading, hence the name Cascading Style Sheets.
|
|
|
|
Given the following CSS:
|
|
|
|
```css
|
|
/* A */
|
|
p.class1[attr='value']
|
|
|
|
/* B */
|
|
p.class1 { }
|
|
|
|
/* C */
|
|
p.class2 { }
|
|
|
|
/* D */
|
|
p { }
|
|
|
|
/* E */
|
|
p { property: value !important; }
|
|
```
|
|
|
|
and the following markup:
|
|
|
|
```xml
|
|
<p style='/*F*/ property:value;' class='class1 class2' attr='value' />
|
|
```
|
|
|
|
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 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 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.
|
|
|
|
## Resources
|
|
|
|
* To run a quick compatibility check, [CanIUse](http://caniuse.com).
|
|
* CSS Playground [Dabblet](http://dabblet.com/).
|
|
* [Mozilla Developer Network's CSS documentation](https://developer.mozilla.org/en-US/docs/Web/CSS)
|
|
* [Codrops' CSS Reference](http://tympanus.net/codrops/css_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)
|