Cascading Style Sheets
Overview
CSS stands for Cascading Style Sheet. HTML tags specify the graphical flow of the elements, be it text, images or flash animations, on a webpage. CSS allows us to define the appearances of those HTML tags with their content, somewhere, so that other pages, if want be, may adhere to. This brings along consistency throughout a website. The cascading effect stipulates that the style of a tag (parent) may be inherited by other tags (children) inside it.
Professional websites separate styling from content. There are many reasons for this, the most obvious (to a developer) being the ability to control the appearance of many pages by changing one file. Styling information includes: fonts, backgrounds, images (that recur on every page), position and dimensions of elements on the page. Your HTML file will now be left with: header information; a series of elements; the text of your website. Because you are creating a Joomla! template, you will actually have: some header information, PHP code to request the rest of the header information, a series of elements, PHP code to request each module position, and PHP code to request the main content.
Style information is coded in CSS and usually stored in files with the suffix .css. A webpage contains a link to the associated .css file so a browser can find the appropriate style information to apply to the page. CSS can also be placed inside a HTML file between <style type="text/css"></style> tags. This is, however, discouraged as it is mixing style and content elements which can make future changes more difficult.
Implementation
Definitions for this section:
- External CSS files
- using <link> in the <head>
- Document head CSS
- using <style> in the <head>
- Inline CSS
- using the style attribute on a tag, i.e. <div style="color:red;">
Guidelines
- External CSS files should be used in preference to document head CSS and document head CSS should be used in preference to inline CSS.
- CSS files MUST have the file extension
.cssand should be stored in the relevant includes directory in the site structure, usually /style/. - The file size of CSS files should be kept as low as possible, especially on high demand pages.
- External CSS must be linked to using the <link> element which must be placed in the head section of the document. This is the preferred method of using CSS. It offers the best experience for the user as it helps prevent FOUC (flash of unstyled content), promotes code reuse across a site and is cacheable.
- External style sheets should not be imported (i.e. using
@import) as it impairs caching. In IE@importbehaves the same as using <link> at the bottom of the page (preventing progressive rendering), so it's best not to use it. Mixing <link> and@importhas a negative effect on browsers' ability to asynchronously download the files. - Document head CSS may be used where a style rule is only required for a specific page.
- Inline styles should not be used.
- Query string data (e.g. "style.css?v=0.1") should not be used on an external CSS file. Use of query strings on CSS files prevents them from caching in some browsers. Whilst this may be desirable for testing, and of course may be used for that, it is very undesirable for production sites.
Directory & Files
Convention places CSS files within a directory named css inside the template directory. While developers are not restricted to this convention, we do recommend it as it helps keep the layout and structure of HUBzero templates consistent. A developer from one project will instantly know where to find certain files and be familiar with the directory structure when working on a project originally developed by someone else.
There are a handful of common CSS files found among most HUBzero. While none of these are required, it is encouraged to follow the convention of including them as it promotes consistency among HUBzero templates and comes with the advantage that certain files, such as main.css are auto-loaded, thus reducing some work on the developer's part.
Here's the standard directory and files for CSS found in a HUBzero template:
/hubzero
/templates
/{TemplateName}
/css
error.css
ie6.css
ie7.css
ie8.css
main.css
print.css
reset.css
File details:
error.css- This is the primary stylesheet loaded by
error.php. ie8.css- Style fixes for Internet Explorer 8.
ie7.css- Style fixes for Internet Explorer 7.
ie6.css- Style fixes for Internet Explorer 6.
main.css- This is the primary stylesheet loaded by
index.php. The majority of your styles will be in here. print.css- Styles used when printing a page.
reset.css- This file is meant to be included before any other CSS file. Its purpose is to reduce browser inconsistencies in things like default line heights, margins and font sizes of headings, and so on.
reset.css
This file is meant to be included before any other CSS file. Its purpose is to reduce browser inconsistencies in things like default line heights, margins and font sizes of headings, and so on.
The reset styles given here are intentionally very generic. There isn't any default color or background set for the <body> element, for example. Colors and any other styling should be addressed in the template's primary stylesheet after loading reset.css.
body,div,dl,dt,dd,ul,ol,li,h1,h2,h3,h4,h5,h6,pre,form,fieldset,input,p,blockquote,th,td {
margin:0;
padding:0;
}
table {
border-collapse:collapse;
border-spacing:0;
}
fieldset,img {
border:0;
}
address,caption,cite,code,dfn,em,strong,th,var {
font-style:normal;
font-weight:normal;
}
ul {
list-style:none;
}
caption,th {
text-align:left;
}
h1,h2,h3,h4,h5,h6 {
font-size:100%;
}
q:before,q:after {
content:'';
}
Typical main.css Structure
main.css controls base styling for your HUB, which is usually further extended by individual component CSS.
We took every effort to organize the main.css in a manner allowing you to easily find a section and a class name to modify. E.g. if you want to change the way headers are displayed, look for "headers" section as indicated by CSS comments. Although you can modify all existing classes, depending on your objectives, it is recommended to avoid modifications to certain sections, as indicated below. While you can add new classes as needed, we caution strongly about removing or renaming any of the existing IDs and classes. Many HUBzero components take advantage of these code styles and any alterations made risk breaking the template display.
Some sections that you are likely to modify:
Body - may want to change site background or font family. Links - pick colors for hyperlinks Headers - pick colors and font size of headings Lists - may want to change general list style Header - you will definitely want to change this Toolbar - display of username, login/logout links etc. Navigation - display of main menu Breadcrumbs - navigation under menu on secondary pages Extra nav - links that appear on the right-hand side in multiple components Footer
Sections where you would want to avoid serious modifications:
Core classes Site notices, warnings, errors Primary Content Columns Flexible Content Columns Sub menu - display of tabs in multiple components
print.css
This is a style sheet that is used only for printing. It removes unnecessary elements such as menus and search boxes, adjusts any background and font colors as needed to improve readability, and can expose link URLs through generated content (advanced browsers only, e.g. Safari, Firefox).
error.css
This is a style sheet that is used only by the error.php layout. It allows for a more custom styling to error pages such as "404 - Page Not Found".
Internet Explorer
We strongly encourage developers to test their templates in as many browsers and on as many operating systems as possible. Most modern browsers will have little differences in rendering, however, Internet Explorer deserves special mention here.
The most widely used browser, Internet Explorer, is also one of the most lacking in terms of CSS support. Internet Explorer has also, traditionally, handled rendering of block elements, element positioning, and other common tasks a bit differently than many other browsers. As can be expected, this has led to much controversy and discussion on how best to handle such differences. We strongly recommend designing for and testing your templates in alternate browsers such as Safari, Firefox, Chrome, or Opera and then applying fixes to Internet Explorer afterwards. We recommend the use of conditional comments to apply special Internet Explorer only stylesheets.
..1a Conditional Comments
Conditional comments only work in Internet Explorer on Windows, and are thus excellently suited to give special instructions meant only for Internet Explorer on Windows. They are supported from Internet Explorer 5 onwards, and it is even possible to distinguish between versions of the browser.
Conditional comments work as follows:
<!--[if IE 6]> Special instructions for IE 6 here <![endif]-->
Their basic structure is the same as an HTML comment (<!-- -->). Therefore all other browsers will see them as normal comments and will ignore them entirely. Internet Explorer, however, recognizes the special syntax and parses the content of the conditional comment as if it were normal page content. As such, they can contain any web content you wish to display only to Internet Explorer. While we're using this feature to load CSS files, it can also be used to load JavaScript or display Internet Explorer specific HTML.
Note: Since conditional comments use the HTML comment structure, they can only be included in HTML, and not in CSS files.
Conditional comments support some variation in syntax. For example, it is possible to target a specific browser version as demonstrated above or target multiple versions such as "all versions of Internet Explorer lower than 7". This can be done with a couple handy operators:
gt= greater thangte= greater than or equal tolt= less thanlte= less than or equal to
<!--[if IE]> According to the conditional comment this is Internet Explorer <![endif]--> <!--[if IE 5]> According to the conditional comment this is Internet Explorer 5 <![endif]--> <!--[if IE 5.0]> According to the conditional comment this is Internet Explorer 5.0 <![endif]--> <!--[if IE 5.5]> According to the conditional comment this is Internet Explorer 5.5 <![endif]--> <!--[if IE 6]> According to the conditional comment this is Internet Explorer 6 <![endif]--> <!--[if IE 7]> According to the conditional comment this is Internet Explorer 7 <![endif]--> <!--[if IE 8]> According to the conditional comment this is Internet Explorer 8 <![endif]--> <!--[if gte IE 5]> According to the conditional comment this is Internet Explorer 5 and up <![endif]--> <!--[if lt IE 6]> According to the conditional comment this is Internet Explorer lower than 6 <![endif]--> <!--[if lte IE 5.5]> According to the conditional comment this is Internet Explorer lower or equal to 5.5 <![endif]--> <!--[if gt IE 6]> According to the conditional comment this is Internet Explorer greater than 6 <![endif]-->
So, to load stylesheets to specific versions of Internet Explorer in our template we do something like the following:
<html>
<head>
... other CSS files ...
<!--[if IE 7]>
<link rel="stylesheet" type="text/css" media="screen" href="{TemplatePath}/{TemplateName}/css/ie7.css" />
<![endif]-->
<!--[if lte IE 6]>
<link rel="stylesheet" type="text/css" media="screen" href="{TemplatePath}/{TemplateName}/css/ie6.css" />
<![endif]-->
</head>
...
</html>
Note: Conditional comments used CSS for should be placed inside the <head> tag of a template after all other CSS have been linked for their affects to properly take place.
Loading From An Extension
Components
Often a component will have a style sheet of its own. Pushing CSS to the template from a component is quite easy and involves only two lines of code.
ximport('Hubzero_Document');
Hubzero_Document::addComponentStylesheet('com_example');
First, we load the Hubzero_Document class. Next we call the static method addComponentStylesheet, passing it the name of the component as the first (and only) argument. This will first check for the presence of the style sheet in the active template's overrides. If found, the path to the overridden style sheet will be added to the array of style sheets the template needs to include in the <head>. If no override is found, the code then checks for the existence of the CSS in the component's directory. Once again, if found, it gets pushed to the template.
Modules
Loading CSS from a module works virtually the same as loading from a component save one minor difference in code. Instead of calling the addComponentStylesheet method, we call the addModuleStylesheet method and pass it the name of the module.
ximport('Hubzero_Document');
Hubzero_Document::addModuleStylesheet('mod_example');
Plugins
Loading CSS from a plugin works similarly to loading from a component or module but instead we call the addPluginStylesheet method and pass it the name of the plugin group and the name of the plugin.
ximport('Hubzero_Document');
Hubzero_Document::addPluginStylesheet('examples', 'test');
Plugin CSS must be named the same as the plugin and located within a directory of the same name as the plugin inside the plugin group directory.
/plugins
/examples
/test
test.css
test.php
test.xml
Further Help
Resources for learning and sharpening CSS skills: