CSS introduction

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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.

Why Use CSS?

CSS is used to define styles for your web pages, including the design, layout and variations in display for different devices and screen sizes.

CSS Syntax

A CSS comprises of style rules that are interpreted by the browser and then applied to the corresponding elements in your document. A style rule set consists of a selector and declaration block.

h1 { //Where h1 is the Selector
Color: red;
margin: blue; // Margin is the Property and red is the value.
}
  • The selector points to the HTML element you want to style.
  • The declaration block consist of 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.
p {
color: red;
text-align: center;
}

In the example above all <p> elements will be center-aligned, with a red text color.

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).

p {
text-align: center;
color: red;
}

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":

#para1 {
text-align: center;
color: red;
}
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:

.center {
text-align: center;
color: red;
}
Note: A class name cannot start with a number!

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:

p {
color: red;
/* This is a single-line comment */
text-align: center;
}
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