Once you have added CSS to your pages, you will want to validate them.
The W3C has an online validator for your CSS as well as its HTML validators.
This link creates a new window to the CSS validator:
http://jigsaw.w3.org/css-validator/
The CSS validator page allows you to check an online page via its URL, upload a local file for validation, or cut and paste some CSS code to see if it validates.
To add a text link from your page to the validator, use this code:
<a href="http://jigsaw.w3.org/css-validator/check/referer">Validate CSS</a>
For combo HTML and CSS validation links use:
<p>
<!-- validator code using text links -->
<a href="http://validator.w3.org/check/referer">Validate
HTML</a>
<a href="http://jigsaw.w3.org/css-validator/check/referer">
Validate CSS</a>
<!-- end validator code using text links -->
</p>
Of course, these link only work when the page is uploaded to the server.
Note that when you use the CSS validator to check a page that does not have a link to an external style sheet and does not contain an internal style sheet, you will get a warning that says: "No style sheet found." This is OK; it will still check any local styles. But if you get the "No style sheet found" warning and you are linking to an external style sheet, then your path to the external style sheet is incorrect.
If you use CSS to specify the color of an element, you should also use CSS
to specify the element's background color. If you don't want to specify a custom
background color, you can use:
background-color: transparent