# A-level Computing/AQA/Computer Components, The Stored Program Concept and the Internet/Webpage Design/HTML & style sheets

In HTML it is possible to add colours, fonts and other styles to the web pages that you build, however this is not recommended and HTML should be used for structure only. To add colours, fonts, etc. we will use Cascading Style Sheets, also known as CSS.

## Style rules

A style sheet is made up of Style Rules. Each Style Rule has three parts, a selector, a property and a value:
selector {property : value}
For multiple properties you separate them using a semicolon;
selector {property1 : value1; property2 : value2}

## Selectors

selector {property : value} You need to know three types of selector:
* type, selects all elements of a certain type on the page e.g. h1 { color : green} selects all the heading 1s and turns them green
* class, selects all elements of the class you have specified and applies the style to only those elements .classname { color : red}
* ID, selects the item with the single ID that you have specified #idname { color : blue }. You can only apply an ID once in an HTML document
| CSS Property | Description | CSS Values | Example for Heading 1 | Output |
| font-style: | Changes the font style of text elements | normal, italic, oblique | h1 { font-style : italic } | Hello |
| font-weight: | Define how bold text is | bold, normal, 400 | h1 { font-weight : bold } | Hello |
| background-color: | Define page or item background colour | green, brown, yellow | h1 { background-color : yellow } | Hello |
| text-align: | horizontal position of text | center, left, right | h1 { text-align : center } | Hello |
| font-family: | define the font of page text | "Times New Roman", Arial, Helvetica | h1 { font-family : "Times New Roman" } | Hello |
| font-size: | define the size of page text | 100%, 250%, 50% | h1 { font-size : 250% } | Hello |
| color: | changes the foreground colour of an element | green, brown, orange | h1 { color : green } | Hello |
| (EXTENSION) text-decoration: | Allows for underlining, strikethrough etc. | overline, underline, line-through | h1 { text-decoration : underline } | Hello |
* Exercise: CSS rules
* Write CSS rules to do the following:
* Turn all heading 3s blue:
* Answer:
* h3 { color : blue}
* Turn all paragraphs red and itallic:
* Answer:
* p { color : red; font-style : italic}
* Turn all class=bbold: bold and blue
* Answer:
* .bbold { color : blue; font-weight: bold}
* Turn all class=uit: underlined and italic
* Answer:
* .uit { text-decoration : underline; font-style : italic }
* Name the three components of a CSS style rule:
* Answer:
* selector {property: value}
* Name the three different types of selector and describe each:
* Answer:
* type, selects all elements of a certain type on the page e.g. h1 { color : red}
* class, selects all elements of the class you have specified and applies the style to only those elements .classname { color : white}
* ID, selects the item with the single ID that you have specified #idname { color : blue}
* Describe the difference between HTML and CSS:
* Answer:
* HTML - Used for page structure
* CSS - a collection of rules about how to present an HTML document

### Type

Take the HTML behind a simple website:
As we probably know, this would build the following page:
Welcome
This is my amazing website, look how great it is!
I doubt you could find a better one anywhere on the web.
Seriously!
You might think my claims are a little over the top, but we could try to make the site better by adding some colour to the title using the following CSS rules:
We can't just place this directly into the page, we have to create a new section inside the <head> </head> tags, this is called embedding CSS, we'll look at another method, External Style Sheets later:
What this will do is change the heading to green, and change each paragraph to red and italic:
{{{2}}}
Exercise: CSS Type Selectors
For the HTML code below, show what the output would be for each set of CSS rules:
<html>
<head>
<title>My Website2</title>
</head>
<body>
<h1>Contact Details</h1>
<p>Please use the details below to get in contact</p>
<h2>Telephone</h2>
<p>Home: 0101010101010<br />
Mobile: 1010101010101<br />
</p>
<h2>Email</h2>
<p>1010101@10100101.com</p>
</body>
</html>
What would these two rules produce?
h2 { color : red }
h1 { color : blue; text-decoration : underline }
Answer:
   My Website2
Address 
{{{2}}}
What would these two rules produce?
p { font-weight : bold }
h1 { font-style : italic }
Answer:
   My Website2
Address 
Contact Details
Telephone
Please use the details below to get in contact
Home: 0101010101010
Mobile: 1010101010101
Email
1010101@10100101.com
Write rules to produce the following output:
   My Website2
Address 
{{{2}}}
Answer:
h1 { color : red; }
h2 { text-decoration : underline}
Write rules to produce the following output:
   My Website2
Address 
Contact Details
Telephone
Home: 0101010101010
Mobile: 1010101010101
Email
1010101@10100101.com
Answer:
h1 { background-color : yellow; }
h2 { text-decoration : underline }
p { background-color : red} :

### Class

Take another look at the HTML behind a simple website:
As you can see there are classes attached to some of the HTML tags, namely the 'textb' and 'texts' classes. On their own they don't do anything, we need to write some CSS style rules to make them come to life, remember that a class selector starts with a (.).
{{{2}}}
Exercise: CSS Class Selectors
For the HTML code below, show what the output would be for each set of the CSS rules:
<html>
<head>
<title>My Website3</title>
</head>
<body>
<h1 class="txtt">Contact Details</h1>
<p>Please use the details below to get in contact</p>
<h2 class="txtg">Telephone</h2>
<p class="txtt">Home: 0101010101010<br />
Mobile: 1010101010101<br />
</p>
<h2>Email</h2>
<p class="txtg">1010101@10100101.com</p>
</body>
</html>
What would these two rules produce?
.txtg { color : blue }
Answer:
note that class="txtt" does nothing as the CSS doesn't define it.
   My Website3
Address 
{{{2}}}
.txtg { color : red }
.txtt { text-decoration : underline; color : green }
Answer:
   My Website3
Address 
Contact Details
Telephone
Home: 0101010101010 Mobile: 1010101010101
Email
1010101@10100101.com :

### ID

Take yet another look at the HTML behind a simple website:
As you can see, I have assigned an id to each of the paragraphs, this means that I can now style them separately from each other. Remember that an ID selector starts with a #.
{{{2}}}
Each id rule applies to a different paragraph, unfortunately I set #para2 to white, so you can't see it!
Exercise: CSS ID Selectors
For the HTML code below, show what the output would be for each set of the CSS rules:
<html>
<head>
<title>My Website3</title>
</head>
<body>
<h1 id="main">Contact Details</h1>
<p>Please use the details below to get in contact</p>
<h2>Telephone</h2>
<p>Home: 0101010101010<br />
Mobile: 1010101010101<br />
</p>
<h2>Email</h2>
<p id="txthighlight">1010101@10100101.com</p>
</body>
</html>
What would these two rules produce?
#main{ color : green }
#txthighlight{ background-color : yellow }
Answer:
   My Website3
Address 
{{{2}}}
Write the CSS to produce the following:
   My Website3
Address 
Contact Details
Telephone
Home: 0101010101010
Mobile: 1010101010101
Email
1010101@10100101.com
Answer:
#main{ font-style : italic }
#txthighlight{ text-align : center } :

## Style sheets (Cascading Style Sheets or CSS)

You should be pretty comfortable with the use of CSS rules, we are now going to look how these rules are linked with the HTML. As we know the style (CSS) of a web page’s contents should to be separated from its structure (HTML), and when these two things come together, it creates the page that you see in your web browser. There are two methods of linking style to structure that you need to know:
* Embedded style, blocks of CSS information inside the HTML document
* External style sheets, i.e., a separate CSS file referenced from the HTML document

### Embedded style

Blocks of CSS information inside the HTML document. You can see that inside the head tag we have a block of CSS that applies to the HTML below it:

### External style sheets

External style sheets use a separate file to store the style information (a .css file) and link the file from inside the HTML document.
As you can see above the HTML file links to the CSS file through the line:
. You could get an HTML page to link to multiple CSS files and link a CSS file from multiple HTML files.
External style sheets are a better way of linking CSS to HTML than embedding CSS in HTML as you can:
* Exercise: Types of style sheet
* Name the two different style sheets:
* Answer:
* external
* embedded
* (there is also inline but it's not pretty to use and not in the syllabus)
* Why might you prefer to use external style sheets on a large web site?
* Answer:
* You can link the same style sheet from multiple pages and changes to the site style would only require changes to that one style sheet
* Extension:CSS3
* There is an awful lot more to learn about CSS and a new version is currently being released alongside HTML5. Don't get left behind, learn all about CSS2 and CSS3 at w3schools.