Okay, unfortunatly there's no quick answer, so here's my best shot:

Custom style sheets allow you to control what is shown, how it is shown, and where it is shown. This applies to text, images, tables, the body of the page and more.

!!!IMPORTANT!!!
Do not add the <style type="text/css"></style> tags!
They are added automatically. All tags you enter will be removed!

Okay, so..

Here are a couple examples:

This will set your background to an image on another server:

body {
background-image: url("http://www.someserver.com/myimage.jpg")
}

This one is the same, but tells it not to tile the image, and to make it fixed:

body {
background-image: url("http://www.someserver.com/myimage.jpg");
background-repeat: no-repeat;
background-attachment: fixed
}

This makes the class labeled "Heading" bold, Arial font, Red color, and underlined:

.Heading{
color: #FF0000;
font-family: Arial;
font-weight: bold;
font-decoration: underlined
}

There are so many things you can do, there's no way I could list them all. You're really limited to what you can imagine for the most part. Here are a couple good links to help you out no matter how much of a n00b (novice) or L337 H4X0r you are:

http://www.w3schools.com/css/default.asp

http://www.w3.org/TR/REC-CSS2/ <- Official site

http://www.w3.org/MarkUp/Guide/Style  <- Has cool color tool

http://www.mompswebdesign.com/jscript/scbarcolor.html <- Scroll Bar Color Generator

Now, besides the classes that you can play with you can also play around with all of the <DIV> tags. With these, you can set their location and layering with positioning attributes and z-index attributes. Just run a Google search for more info here.

Here is a quick <DIV> example that modifies the "LastTen" ID:

This move the Last Ten block to the top left corner 200px from the left and 200px from the top and sets the width of the thing to 200px. Z-Index is it's layer to put it on top of everything else:

#LastTen{
position:absolute;
left:200;
width:200;
top:200;
z-index:200
}

This will hide the "LastTen" block all together:

#LastTen{
visibility: hidden
}

Here's a list of all the classes that I have made for you to play with:

.button
.textbox
.NameHeading
.Blurb
.BlurbHeading
.ProfileMessagesHeading
.ProfileMessageText
.LeaveAMessage
.JournalHeading
.JournalText
.JournalSmallText
.JournalShowHideText
.JournalViewAll
.StuffHeading
.StuffLabel
.StuffInfo
.MoreStuffHeading
.MoreStuffLabel
.MoreStuffInfo
.PierceLink
.TatLink
.HCLink
.StudioLink
.MoreStuffQuote
.MoreStuffMoviesLink
.SomeMoreStuffHeading
.SomeMoreStuffLabel
.SomeMoreStuffInfo
.BuddyHeading
.BuddyLabel
.BuddyInfo
.VotingHeading
.VotingLabel
.VotingInfo
.LastTenHeading
.LastTenLink
.JournalCommentHeading
.JournalComment
.JournalCommentIcon
.ProfilePhoto
.AvatarImage
.text
.bold
.alerttext
.smtext
.smalltext
.SmLink

They're pretty self-describable, but if you can't figure one out, just change it to something and look for the change =)

Here is a list of all the <DIV> id's that you can mess with:

NameHeading
ProfilePhoto
ProfilePhotoCaption
ProfilePhotoUpload
Blurb
UploadBGImage
AddStyles
ProfileMessages
ProfileMessagesIndiv
Journal
JournalComments
JournalCommentShowHide
Stuff
MoreStuff
Quote
Movies
SomeMoreStuff
Avatar
ILikeThemImages
TheyLikeMeImages
BuddyModIcon
Voting
LastTen

Once again, you can prolly guess what they each control by their name.

After you add your style sheet to your profile, make sure that you turn it on (Check "Yes" under the style sheet box). Should you choose to go back to the default settings, you can just change the toggle back to "No". This will NOT erase your style sheet. You can just turn it back on later if you want.

If you want something to compare to, here is the style sheet that I use for this site:

http://www.BodyMod.org/modstyle.css

It's not complex at all, so it should be helpful.

If anyone would like to add to this to help people out, make any corrections to something I've said, or show off your own style sheets you're using here, please post them here so everyone can see!

Thanks, and have fun!

.: Adam

the #FFFFFF and such are hex for colors. They're the Hex value for RGB's. The first two represent red 00(none) -> FF(all), second, green, third blue.

Here's a cool hex color chart.

Hope this helps ya out =)

.: Adam

you broke it :O

ok,no, sorry i dont know, ill go now :P