Every web designer has to deal with CSS, day after day. Here are some links and resources found on the web, that should help you to improve your CSS skills.
1 – Flexible CSS Layouts

Keeping your content in order of priority with flexible CSS layouts: This article shows you how to use CSS floats to achieve any column layout, while keeping your most important content highest on the page.
2 – CSS Sticky Footer

CSS Sticky Footer Layout: A CSS Sticky Footer method that actually sticks to the bottom of the page.
3 – CSS Image Maps

CSS Image Maps: A sample image map that’s built entirely using CSS and XHTML, without any Javascript.
4 – CSS Drop Shadows

CSS Drop Shadows: A technique to build flexible CSS drop shadows that can be applied to arbitrary block elements, that can expand as the content of the block changes shape, compatible with most modern browsers and with better results for standards-compliant browsers.
5 – Creating Custom Corners And Borders

CSS Design: Creating Custom Corners & Borders: How to apply customized borders and corners to liquid CSS layouts

CSS Design: Creating Custom Corners & Borders Part II: The technique to use patterned or gradient backgrounds
5 – Link Display for Print

Improving Link Display for Print: A technique to collect all of the URIs referenced (hrefs and citations) in a specific container within the page (after all, we probably don’t want to grab the navigation, etc.), place the links (minding the duplicates) into an ordered list which can be dropped into an id-ed container of our choosing, and supply each reference with the corresponding footnote number as a superscript.
6 – Customized input elements

Fun with forms – customized input elements: How to apply customized backgrounds to HTML forms, while preserving structurally clean markup and accessibility.
7 – Custom bullets

CSS tricks for custom bullets: Using the background property for styling links, bulleted lists, and more.
8 – Styled images with caption

Styled images with caption: How do you balance the need for easy update by web editors with the desire to make a site as visually appealing as possible by combining CSS and DOM scripting.
9 – CSS Production Notes

A Message To You, Rudy – CSS Production Notes: A technique that places your page production notes in one convenient place within an XHTML document and uses nothing more than meaningful markup and CSS.
10 – CSS Based Navigation

CSS Based Navigation: An example of a nice CSS based navigation bar.
11 – CSS Tabs

Free CSS Navigation Menu Designs: Some example of simple CSS navigation menus.
12 – CSS Dock Menu

CSS Dock Menu: A Mac-like CSS dock menu made with Jquery Javascript library, Fisheye component from Interface and some icons
13 – Tree lists

Turning Lists into Trees: A technique to display a multi-level unordered list in the form of a tree with lines connecting nodes.