What is CSS?
What is CSS?
------------
<> CSS stands for Cascading Style Sheets
<> Styles define how to display HTML elements
<> Styles were added to HTML 4.0 to solve a problem
<> External Style Sheets can save a lot of work
<> External Style Sheets are stored in CSS files
CSS defines HOW HTML elements are to be displayed.
Styles are normally saved in external .css files. External style sheets enable you to change the appearance and layout of all the pages in a Web site, just by editing one single file!
CSS Example:
--------------
CSS declarations always ends with a semicolon, and declaration groups are surrounded by curly brackets:
p {color:red;text-align:center;}
To make the CSS more readable, you can put one declaration on each line, like this:
Example:
--------
p
{
color:red;
text-align:center;
}
CSS Comments:
------------
Comments are used to explain your code, and may help you when you edit the source code at a later date. Comments are ignored by browsers.
A CSS comment begins with "/*", and ends with "*/", like this:
/*This is a comment*/
p
{
text-align:center;
/*This is another comment*/
color:black;
font-family:arial;
}
CSS Id and Class
The id and class Selectors:
---------------------------
In addition to setting a style for a HTML element, CSS allows you to specify your own selectors called "id" and "class".
The id Selector:
---------------------------
The id selector is used to specify a style for a single, unique element.
The id selector uses the id attribute of the HTML element, and is defined with a "#".
The style rule below will be applied to the element with id="para1":
Example
#para1
{
text-align:center;
color:red;
}
Note: Do NOT start an ID name with a number! It will not work in Mozilla/Firefox.
The class Selector:
---------------------------
The class selector is used to specify a style for a group of elements. Unlike the id selector, the class selector is most often used on several elements.
This allows you to set a particular style for any HTML elements with the same class.
The class selector uses the HTML class attribute, and is defined with a "."
In the example below, all HTML elements with class="center" will be center-aligned:
Example
----------
.center {text-align:center;}
You can also specify that only specific HTML elements should be affected by a class.
In the example below, all p elements with class="center" will be center-aligned:
Example
-----------
p.center {text-align:center;}
Do NOT start a class name with a number! This is only supported in Internet Explorer
3 Ways to Insert CSS
There are three ways of inserting a style sheet:
------------------------------------------------
External style sheet
Internal style sheet
Inline style
External Style Sheet
An external style sheet is ideal when the style is applied to many pages. With an external style sheet, you can change the look of an entire Web site by changing one file. Each page must link to the style sheet using the <link> tag. The <link> tag goes inside the head section:
<head>
<link rel="stylesheet" type="text/css" href="mystyle.css" />
</head>
An external style sheet can be written in any text editor. The file should not contain any html tags. Your style sheet should be saved with a .css extension. An example of a style sheet file is shown below:
hr {color:sienna;}
p {margin-left:20px;}
body {background-image:url("images/back40.gif");}
Do not leave spaces between the property value and the units! "margin-left:20 px" (instead of "margin-left:20px") will work in IE, but not in Firefox or Opera.
Internal Style Sheet
-----------------------------------
An internal style sheet should be used when a single document has a unique style. You define internal styles in the head section of an HTML page, by using the <style> tag, like this:
<head>
<style type="text/css">
hr {color:sienna;}
p {margin-left:20px;}
body {background-image:url("images/back40.gif");}
</style>
</head>
Inline Styles
-----------------------------
An inline style loses many of the advantages of style sheets by mixing content with presentation. Use this method sparingly!
To use inline styles you use the style attribute in the relevant tag. The style attribute can contain any CSS property. The example shows how to change the color and the left margin of a paragraph:
<p style="color:sienna;margin-left:20px">This is a paragraph.</p>
Multiple Style Sheets
-------------------------------
If some properties have been set for the same selector in different style sheets, the values will be inherited from the more specific style sheet.
For example, an external style sheet has these properties for the h3 selector:
h3
{
color:red;
text-align:left;
font-size:8pt;
}
And an internal style sheet has these properties for the h3 selector:
h3
{
text-align:right;
font-size:20pt;
}
If the page with the internal style sheet also links to the external style sheet the properties for h3 will be:
color:red;
text-align:right;
font-size:20pt;
The color is inherited from the external style sheet and the text-alignment and the font-size is replaced by the internal style sheet.
Multiple Styles Will Cascade into One
-------------------------------------
Styles can be specified:
inside an HTML element
inside the head section of an HTML page
in an external CSS file
Tip: Even multiple external style sheets can be referenced inside a single HTML document.
Cascading order
----------------
What style will be used when there is more than one style specified for an HTML element?
Generally speaking we can say that all the styles will "cascade" into a new "virtual" style sheet by the following rules, where number four has the highest priority:
Browser default
External style sheet
Internal style sheet (in the head section)
Inline style (inside an HTML element)
So, an inline style (inside an HTML element) has the highest priority, which means that it will override a style defined inside the <head> tag, or in an external style sheet, or in a browser (a default value).
Note: If the link to the external style sheet is placed after the internal style sheet in HTML <head>, the external style sheet will override the internal style sheet!
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