Xah Lee, 2009-01-16, 2011-08-17
Cascading Style Sheet (CSS), is a markup language that allows you to specify appearances of HTML. This page shows you the practical basics.
To add CSS in your HTML file, do like this:
<head> <link rel="stylesheet" type="text/css" href="mystyle.css"> <title>My Title</title> </head>
In the above example,
whenever the HTML file is loaded, it will load the file 〔mystyle.css〕.
The <link …> line must be inside the “head” tag.
If you use the above for all your files, then you can control your whole site's appearance by modifying the single CSS file.
If you want to use CSS only for a single file, you can embed it in HTML file's header using the
<style> tag,
like this:
<head> <title>My Title</title> <style type="text/css"> p {color:red} /* more CSS code here */ </style> </head>
We'll cover the actual CSS syntax later in this page.
If you want to specify a style only for one particular HTML tag in a HTML file, you can embed a attribute style="…" inside the tag, like this:
<p>… this is <span style="color:red">important!</span></p> <p style="color:red">This whole paragraph is red import!.</p>
A CSS source code looks like this:
p {line-height:125%; width:60ex; font-family:sans-serif} li {margin-top:0.8ex; color:gray} blockquote {color:blue} img {border:solid thin black} /* basic table style with border */ table.normal {border:1px solid black;border-collapse:collapse;} table.normal th, table.normal td {border:1px solid gray;padding:.5ex} /* for programing language source code */ span.code {font-family:monospace;color:#00008d}
In the above example, it says that any “p” tag's content (a paragraph) will have a line height that's 125% of default, and has a width of 60 “ex”, and the font used will be sans-serif such as Arial. (See: Common Web Fonts on Windows and Mac.)
Similiarly, other tags's appearance are also specified. (the “ex” is the font's x-height. A width of 60ex will render each line's width at about 65 to 70 chars.)
In general, CSS code has lines like this:
‹tag matcher› {‹appearance spec›}
The tag matcher is technically called Selector.
The tag matcher is often just the tag's name, but it can also be specified for tags that has a particular “class” attribute, or tags with a particular “id” attribute, or tags that are child of another tag, and others. For example, if you have <p class="warning">…</p> for any important paragraph, you can make all such paragraph red by p.warning {color:red}.
/* basic examples of tag matching */ p {color:red} /* match any “p” tag */ p.xyz {color:red} /* match p tags that have “class="xyz"”. */ p#xyz {color:red} /* match the “p” tag that has “id="xyz"”. */ div > p {color:red} /* match “p” that's immediate child of “div”. */ div p {color:red} /* match “p” that's nested in “div” however deep. */ span.booktitle {color:red} /* match “span” tags with “class="booktitle"”. */ .bold {font-weight:bold} /* match any tag with “class="bold"”. */ a.offsite {font-size:small} /* match any link tag “a” with “class="offsite"”. */
Some 95% of CSS can be mastered in just a few days. Complete mastery of what CSS can and cannot do, and how to use it properly for web design, details of CSS2 and CSS3, browser quirks, will usually take a year or more of experience.
As of 2011-08, all latest version of major browsers supports all of CSS level 2.1, and some of CSS3. For latest status, see: Comparison of layout engines (Cascading Style Sheets).
Firefox, Google Chrome, and other browsers have tools that validate CSS. Some are builtin, some are extensions. You can try this one for Firefox: Web Developer 1.1.8 Add-on by Chrispederick. This is a absolutely wonderful tool for any coders of HTML/CSS. Make sure the CSS you create is valid.
For a detailed tutorial on tag matching, see: CSS Tag Matching (Selector) Syntax.
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