Want to become an expert in CSS? Here are some of the best resources I've found 'round the web.
A step-by-step guide to CSS basics. Go here if you're comfortable with basic HTML.
Various odds-and-sods building on the basics of CSS.
Exploiting the versatile depths of CSS.
all
background
background-attachment
background-clip
background-color
background-image
background-origin
background-position
background-repeat
background-size
border
border-bottom
border-bottom-color
border-bottom-left-radius
border-bottom-right-radius
border-bottom-style
border-bottom-width
border-collapse
border-color
border-image
border-image-outset
border-image-repeat
border-image-slice
border-image-source
border-image-width
border-left
border-left-color
border-left-style
border-left-width
border-radius
border-right
border-right-color
border-right-style
border-right-width
border-spacing
border-style
border-top
border-top-color
border-top-left-radius
border-top-right-radius
border-top-style
border-top-width
border-width
bottom
box-shadow
caption-side
clear
clip
color
content
counter-increment
counter-reset
cursor
direction
display
empty-cells
float
font
font-family
font-size
font-size-adjust
font-stretch
font-style
font-synthesis
font-variant
font-weight
height
left
letter-spacing
line-height
list-style
list-style-image
list-style-position
list-style-type
margin
margin-bottom
margin-left
margin-right
margin-top
max-height
max-width
min-height
min-width
opacity
orphans
outline
outline-color
outline-style
outline-width
overflow
padding
padding-bottom
padding-left
padding-right
padding-top
page-break-after
page-break-before
page-break-inside
position
quotes
right
table-layout
text-align
text-decoration
text-decoration-color
text-decoration-line
text-decoration-style
text-indent
text-transform
top
transform
transform-origin
transition
transition-delay
transition-duration
transition-property
transition-timing-function
unicode-bidi
vertical-align
visibility
white-space
widows
width
word-spacing
z-index