Using the CSS
What is CSS? CSS is a language that’s used to define the formatting applied to a Website, including colors, background images, typefaces (fonts), margins, and indentation. Let’s look at a basic example to see how this is done. <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" " A Simple Page h1, h2 { font-family: sans-serif; color: #3366CC; } First Title … Second Title … Third Title …
Using CSS in HTML lnline Styles The simplest method of adding CSS styles to your web pages is to use inline styles. An inline style is applied via the style attribute, like this: Inline styles have two major disadvantages: 1)They can’t be reused. For example, if we wanted to apply the style above to another p element, we would have to type it out again in that element’s style attribute. 2)Additionally, inline styles are located alongside the page’s markup, making the code difficult to read and maintain. Amazingly few discotheques provide jukeboxes.
Using CSS in HTML Embedded Styles In this approach, you can declare any number of CSS styles by placing them between the opening and closing tags, as follows: While it’s nice and simple, the tag has one major disadvantage: if you want to use a particular set of styles throughout your site, you’ll have to repeat those style definitions within the style element at the top of every one of your site’s pages. CSS Styles here
Using CSS in HTML External Style Sheets An external style sheet is a file (usually given a.css filename) that contains a web site’s CSS styles, keeping them separate from any one web page. Multiple pages can link to the same.css file, and any changes you make to the style definitions in that file will affect all the pages that link to it. To link a document to an external style sheet (say, styles.css), we simply place a link element in the document’s header:
CSS Selectors Every CSS style definition has two components: A list of one or more selectors, separated by commas, define the element or elements to which the style will be applied. The declaration block specifies what the style actually does.
CSS Selectors Type Selectors By naming a particular HTML element, you can apply a style rule to every occurrence of that element in the document. For example, the following style rule might be used to set the default font for a web site: p, td, th, div, dl, ul, ol { font-family: Tahoma, Verdana, Arial, Helvetica, sans-serif; font-size: 1em; color: #000000; }
CSS Selectors Class Selectors CSS classes comes in when you want to assign different styles to identical elements that occur in different places within your document. Consider the following style, which turns all the paragraph text on a page blue: Great! But what would happen if you had a sidebar on your page with a blue background? You wouldn’t want the text in the sidebar to display in blue as well—then it would be invisible. What you need to do is define a class for your sidebar text, then assign a CSS style to that class. To create a paragraph of the sidebarclass, first add a classattribute to the opening tag: p { color: #0000FF; } This text will be white, as specified by the CSS style definition below.
CSS Selectors Class Selectors Now we can write the style for this class: This second rule uses a class selector to indicate that the style should be applied to any element of the sidebar class. The period indicates that we’re naming a class—not an HTML element. p { color: #0000FF; }.sidebar { color: #FFFFFF; }
CSS Selectors ID Selectors In contrast with class selectors, ID selectors are used to select one particular element, rather than a group of elements. To use an ID selector, first add an id attribute to the element you wish to style. It’s important that the ID is unique within the document: To reference this element by its ID selector, we precede the id with a hash (#). For example, the following rule will make the above paragraph white: ID selectors can be used in combination with the other selector types. This paragraph is uniquely identified by the ID "tagline". #tagline { color: #FFFFFF; } #tagline.new { font-weight: bold; color: #FFFFFF; }
CSS Selectors Descendant Selectors A descendant selector will select all the descendants of an element. In this case, because our page contains a div element that has a class of sidebar, the descendant selector.sidebar p refers to all p elements inside that div. p { color: #0000FF; }.sidebar p { color: #FFFFFF; } This paragraph will be displayed in white. So will this one.
CSS Selectors Child Selectors A descendant selector will select all the descendants of an element, a child selector only targets the element’s immediate descendants, or “children.” Consider the following markup: This paragraph will be displayed in white. So will this one. If we use a descendant selector, this will be white too. But if we use a child selector, it will be blue.
CSS Selectors Child Selectors In this example, the descendant selector we saw in the previous section would match the paragraphs that are nested directly within div.sidebar as well as those inside div.tagline. If you didn’t want this behavior, and you only wanted to style those paragraphs that were direct descendants of div.sidebar, you’d use a child selector. A child selector uses the > character to specify a direct descendant. Here’s the new CSS, which turns only those paragraphs directly inside.sidebar (but not those within.tagline) white: Note: Unfortunately, Internet Explorer 6 doesn’t support the child selector. p { color: #0000FF; }.sidebar>p { color: #FFFFFF; }
Most Common CSS Mistakes
ID vs. Class What An ID refers to a unique instance in a document, or something that will only appear once on a page. For example, common uses of IDs are containing elements such as page wrappers, headers, and footers. On the other hand, a CLASS may be used multiple times within a document, on multiple elements. A good use of classes would be the style definitions for links, or other types of text that might be repeated in different areas on a page. In a style sheet, an ID is preceded by a hash mark (#), and might look like the following: #header { height:50px; } #footer { height:50px; } #sidebar { width:200px; float:left; } #contents { width:600px; }
ID vs. Class What Classes are preceded by a dot (.). An example is given below..error { font-weight:bold; color:#C00; }.btn{ background:#98A520; font-weight:bold; font-size:90%; height:24px; color:#fff; }
Redundant Units for Zero Values The following code doesn't need the unit specified if the value is zero. It can be written instead like this: Don't waste bytes by adding units such as px, pt, em, etc, when the value is zero. The only reason to do so is when you want to change the value quickly later on. Otherwise declaring the unit is meaningless. Zero pixels is the same as zero points. padding:0px 0px 5px 0px; padding:0 0 5px 0;
Avoid Repetition We should avoid using several lines when just one line will do. For example, when setting borders, some people set each side separately: But why? When each border is the same! Instead it can be like: border-top:1px solid #00f; border-right:1px solid #00f; border-bottom:1px solid #00f; border-left:1px solid #00f; border:1px solid #00f;
Excess Whitespace Usually we have tendency to include whitespace in the code to make it readable. It'll only make the stylesheet bigger, meaning the bandwidth usage will be higher. Of course it's wise to leave some space in to keep it readable.
Grouping Identical Styles together So when we want a same style to a couple of elements. It is good to group them together and define the style instead of defining the style for each element separately. It will also make updating the style much easier. h1, p, #footer,.intro { font-family:Arial,Helvetica,sans-serif; }
Margin vs. Padding As margins and paddings are generally be used interchangeably, it is important to know the difference. It will give you greater control over your layouts. Margin refers to the space around the element, outside of the border. Padding refers to the space inside of the element, within the border. Example: No Padding, 10px Margin Result: p { border: 1px solid #0066cc; margin:10px; padding:0; }
Margin vs. Padding Example: No Margin, 10px Padding Result: p { border: 1px solid #0066cc; padding:10px; margin:0; }