How to create clean and efficient CSS

In a typical workday, I deal with dozens of yahoo stores and very often I have to tweak, fix, or change CSS used by these stores. While some stores have very clean and easy to follow style sheets or CSS definitions, the vast majority of stores I've seen seem to include complete hack jobs, style sheets put together completely haphazardly, or as an afterthought. While working in such a store, the idea came to me to turn my gripes into a post. So the following is my list of dos and don'ts of good CSS or style design.

1. Externalize your style sheets. This means to save your style sheets into one or more css files, and link to them using the <link rel="stylesheet" type="text/css" href="/lib/yourstoreid/yourstyle.css"> notation, or in Editor V3.0, you can use the LINK operator.

2. Combine your style sheets into as few files as possible. Nothing worse than trying to wade through 6, 8, 10 or more different style sheets to find the color of a link for example. If you must use multiple style sheets, at least give them meaningful names. Style1.css, style2.css, mystyles.css, etc. are NOT meaningful. Item.css, section.css, home.css ARE meaningful.

3. If you are using Editor V3.0, you can put your own CSS stuff in the css-edits.css file. You can find it on the “Contents” page.

4. Avoid using inline CSS, that is, putting styling in the style attribute of tags, especially within RTML. Imagine trying to find something like a “style: font-size: 20px” inside one of the store templates if you don't know where it is...

5. Use IDs for elements you know you will only have one. For example, chances are you will only have a single left navigation, so give it an ID, not a class. For instance, <div id="navbar"> ... </div>. Use classes for similar things of which there are more than one on the page.

6. Don't repeat classes without a purpose. So many times I've seen navigation links like this:

<a class="nav" href="index.html">Home</a>
<a class="nav" href="info.html">Info</a>
<a class="nav" href="contents.html">Contents</a>

Instead, do something like this:

<div id="navlinks">
<a href="index.html">Home</a>
<a href="info.html">Info</a>
<a href="contents.html">Contents</a>
</div>

You can now easily define the styles for these links like this:

#navlinks a:link, #navlinks a:visited { ... }
#navlinks a:hover { ... }

7. Start from top to bottom. Define the main styles first, and refine them as you get specific. For example, define your default font like this:
body, * { font-family: arial, Helvetica,sans-serif; font-size: 10pt }
Then, as you define your other elements, you won't have to define the font again, only if you needed to override one or more of the global styles (like font-size, for example).

8. This is related to the previous point: don't redefine the same styles more than once. If you defined your default font to be Arial, don't define it again for, say the <a> tags. This makes things complicated. Remember, CSS was meant to make life easier.

9. Don't use !important, only if you absolutely must. I often see people use !important to fix something, but it's a lazy way of fixing styles. True, if you slap !important on a style definition, it will take precedence over anything else defined for that style up to that point. But once you have your style sheet or style sheets littered with !important lines, trying to fix THAT later can be a nightmare.

10. Don't use chained styles with IDs, for example: #main #maintable #navbar. IDs are unique by definition, so it's perfectly enough to just reference the ID by itself. When you chain IDs like in the above example, you are establishing a stronger rule that says, your style should only apply if #navbar is somewhere within #maintable, and #maintable is somewhere within #main.