You probably have already heard about themes, but you might not know how to incorporate them into your own site.
Commonly, a theme refers to a set of graphics, color, and layout definitions that can be applied to a user interface to give it a specific look and feel. A "theme-able" application lets a user select between different looks of this application.
A well-known representative is Winamp or Netscape 6. The concept of themes is a relatively new and important development in the evolution of modern GUI applications. Themes give users the ability to choose or create individual interfaces easily for enabled applications without the need to recompile them. You might even consider this as an end-user related aspect of the growing open-source idea.
The drawback is that it may not be possible to use CSS in full effect for older 4.x platforms because of erroneous and incomplete CSS support. As a rule of thumb you should only try it with the newest browsers available (IE 5.5, Netscape 6, Opera 5, and Konqueror). The RichInStyle site provides a good list of CSS bugs and support.
Basically any application has to match one important prerequisite to switch between different themes: it must separate the data of the application -- the model -- from the view of the data. Both components are connected and controlled by a controller.
In terms of OOP, this is called the model-view-controller (MVC) concept, Java's GUI toolkit Swing is probably the most famous representative.
After identifying the components, let's specify their roles in relation to our task:
As stated earlier, it's possible to
not pollute your documents with presentational markup elements like
<b>; you should stick to elements like
<strong>. Don't use well-known elements and attributes that give control over the presentation of a document. These are marked as deprecated in HTML 4.01 (which means that they are evil and will be removed in following specifications) and must be replaced by equivalent CSS definitions.
<link>element (see below). A style sheet file which holds the complete definition of the graphical representation is nothing more than a theme file. For activation, we only need one more component that controls everything.
1. Prepare your documents
As explained above, your HTML files should only contain structural markup after the first step. A good place to learn more about separating model and presentation is Jakob Nielsen's UseIt site. Other great places to start are pages about accessible design, such as the Web Content Accessibility Guidelines and the accompanying Techniques for Web Content Accessibility Guidelines.
2. Create themes
This step assumes at least some basic knowledge of the attributes supported in CSS. If you're new to CSS, you should read some introductory material first.
After organizing your information, you're ready to give it a visual representation. You can define styles for a certain element type, classes of elements, and individual elements, and apply them using CSS selectors. With CSS, you can also define elements to become invisible, this allows you to have even greater control over your layouts. It's especially important to identify all parts you want to give distinct views in different themes and to use a clever naming system.
After you create a default stylesheet, just copy it and use it as a template for additional style sheets, or themes. Store all style sheet files in a single common folder. To import a style sheet into an HTML document after creation, you write:
<link rel="stylesheet" type="text/css" href="Path to your style sheet file">
The trick is simply to write into your document while it's being
loaded, a browser will parse this like any other content and load the
defined style sheet file, which is applied to the document:
document.writeln('<link href="'+THEMES_FOLDER_PATH+s+'.css" type="text/css" rel="stylesheet">');
To make this reusable, you have to consider two points. First, of course, you have to wrap it in a function (see
It's very important to use absolute paths -- paths that are
evaluated starting from your document root folder. This is necessary
because you'll have to adjust the path every time you insert the script
into a new document which has a different relative location to your
style sheet files -- which isn't really a reusable script solution.
When you look at the code line above, you'll also find the variable
s, which holds the name of the theme, the file suffix
.css is added statically. Actually,
s should hold one of your theme's name that you stored in the common folder (whose name is specified in
Next we need a method to let users choose between different styles, so we create a reusable function called
setTheme(), which receives the name of a theme as an argument. This is how to call it:
setTheme(), we store the name of the theme with a specified key in our cookies with
SetCookie() after deleting an old value with
DeleteCookie(). To apply the new style sheet, the last step is to reload the current document which is easily done by resetting the current location. Since it comes, in most cases, from your memory cache, we're not generating network noise.
While the document is reloaded
insertStyleSheet() gets called again. Using
GetCookie(), we're trying to access the name of a theme, if specified. If none is found, the script uses a default style and writes the
<link> element into the document, see above.
4. Step: Add the script and correct settings
documents. What we didn't consider so far is what happens to clients
<noscript><link href="/styles/default.css" type="text/css" rel="stylesheet"></noscript>
After you create the snippet with the correct (absolute) paths, you can just cut and paste it anywhere in your site's documents.
You must take care that you always point to the same default style
sheet (in case you're not supplying a style sheet for users without
DEFAULT_THEME, in the script. The last step is to adjust the path to your themes folder in
(be sure to end your path with a slash) and you're done.
As we saw, implementing your own themes is easy as long as you understand the underlying principles and technologies. Also, keep in mind, that CSS support is not as consistent as it should be. For sites with a large audience, you should stick to the old dirty way. While we didn't discuss all the complexities in this article, hopefully, you've become curious for more -- and that's really all I wanted. Stay tuned!