CSS Introduction:
What is CSS?
- CSS stands for Cascading Style Sheets
- CSS describes how HTML elements are to be displayed on screen, paper, or in other media
- CSS saves a lot of work. It can control the layout of multiple web pages all at once
- External stylesheets are stored in CSS files.
CSS Syntax
A CSS rule-set consists of a selector and a declaration block:
The declaration block contains one or more declarations separated by semicolons.
Each declaration includes a CSS property name and a value, separated by a colon.
A CSS declaration always ends with a semicolon, and declaration blocks are surrounded by curly braces.
Example
<!DOCTYPE html>
<html>
<head>
<style>
p {
color: red;
text-align: center;
}
</style>
</head>
<body>
<p>Hello World!</p>
<p>These paragraphs are styled with CSS.</p>
</body>
</html>
Result:
Hello World!These paragraphs are styled with CSS.
CSS Selectors
CSS selectors are used to "find" (or select) HTML elements based on their element name, id, class, attribute, and more.The element Selector
The element selector selects elements based on the element name.You can select all <p> elements on a page like this (in this case, all <p> elements will be center-aligned, with a red text color):
Example:
<html>
<head>
<style>
p {
text-align: center;
color: red;
}
</style>
</head>
<body>
<p>Every paragraph will be affected by the style.</p>
<p id="para1">Me too!</p>
<p>And me!</p>
</body>
</html>
Result:
Every paragraph will be affected by the style.
Me too!
And me!
The id Selector
The id selector uses the id attribute of an HTML element to select a specific element.The id of an element should be unique within a page, so the id selector is used to select one unique element!
To select an element with a specific id, write a hash (#) character, followed by the id of the element.
The style rule below will be applied to the HTML element with id="para1":
Example
<!DOCTYPE html>
<html>
<head>
<style>
#para1 {
text-align: center;
color: red;
}
</style>
</head>
<body>
<p id="para1">Hello World!</p>
<p>This paragraph is not affected by the style.</p>
</body>
</html>
Result:
Hello World!
This paragraph is not affected by the style.Note: An id name cannot start with a number!
The class Selector
The class selector selects elements with a specific class attribute.To select elements with a specific class, write a period (.) character, followed by the name of the class.
In the example below, all HTML elements with class="center" will be red and center-aligned:
Example
<!DOCTYPE html>
<html>
<head>
<style>
.center {
text-align: center;
color: red;
}
</style>
</head>
<body>
<h1 class="center">Red and center-aligned heading</h1>
<p class="center">Red and center-aligned paragraph.</p>
</body>
</html>
Result:
Red and center-aligned heading
Red and center-aligned paragraph.
In the example below, only <p> elements with class="center" will be center-aligned:
Example:
<!DOCTYPE html>
<html>
<head>
<style>
p.center {
text-align: center;
color: red;
}
</style>
</head>
<body>
<h1 class="center">This heading will not be affected</h1>
<p class="center">This paragraph will be red and center-aligned.</p>
</body>
</html>
Result:
This heading will not be affected
This paragraph will be red and center-aligned.
In the example below, the <p> element will be styled according to class="center" and to class="large":
Example:
<!DOCTYPE html>
<html>
<head>
<style>
p.center {
text-align: center;
color: red;
}
p.large {
font-size: 300%;
}
</style>
</head>
<body>
<h1 class="center">This heading will not be affected</h1>
<p class="center">This paragraph will be red and center-aligned.</p>
<p class="center large">This paragraph will be red, center-aligned, and in a large font-size.</p>
</body>
</html>
Result:
This heading will not be affected
This paragraph will be red and center-aligned.
This paragraph will be red, center-aligned, and in a large font-size.
Note: A class name cannot start with a number!
Grouping Selectors
If you have elements with the same style definitions, like this:
h1
{
text-align: center;
color: red;
}
h2
{
text-align: center;
color: red;}
p
{
text-align: center;
color: red;
}
To group selectors, separate each selector with a comma.
In the example below we have grouped the selectors from the code above:
Example:
<!DOCTYPE html>
<html>
<head>
<style>
h1, h2, p {
text-align: center;
color: red;
}
</style>
</head>
<body>
<h1>Hello World!</h1>
<h2>Smaller heading!</h2>
<p>This is a paragraph.</p>
</body>
</html>
Result:
Hello World!
Smaller heading!
This is a paragraph.
CSS Comments
Comments are used to explain the code, and may help when you edit the source code at a later date.Comments are ignored by browsers.
A CSS comment starts with /* and ends with */. Comments can also span multiple lines:
Example:
<!DOCTYPE html>
<html>
<head>
<style>
p {
color: red;
/* This is a single-line comment */
text-align: center;
}
/* This is
a multi-line
comment */
</style>
</head>
<body>
<p>Hello World!</p>
<p>This paragraph is styled with CSS.</p>
<p>CSS comments are not shown in the output.</p>
</body>
</html>
Result:
Hello World!
This paragraph is styled with CSS.
CSS comments are not shown in the output.
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