Alright, here is a tutorial on one of the easiest Coding ways ever!
CSSCSS Stands for Cascading Style Sheet.
You see it on every single website there is

CSS is the looks of the Site your on. The Background, Font, font color, width, height, and so on, is all in CSS.
So, How do you start using CSS?
Simply just start with the Style Tags (You do'nt need them if your going to code CSS for SMF for Free).
<style>
</style>
Now, To the Accuall CSS Part. First, you need to designate which items will be effected:
<style>
body
.class
#id
</style>
In the Above coding, you have three diffrent ways you can add styles to things. "body" is a tag. You can use any tag though, such as table, tr, td, span, div, a and so on.
.class is the class of the object. The object must has a class='CLASS_NAME' in the tag for that class to work. In CSS, you can recognize a class by a period at the begginning of the name.
#id is the ID of the object. Just like Class, you need id="ID_NAME" in the tab name for it to work. The Number sign at the beggning recognizes it as a ID.
Now, to add the diffrent thing you can do with it:
<style>
body {
}
.class {
}
#id {
}
</style>
You must have the brackets in order for the CSS to actually do anything for that element. The Brackets are { or }. That is where all the information will be going:
<style>
body {
background-color: red;
}
.class {
background: url(Insert_URL);
}
#id {
width: 400px;
height: 100px;
}
</style>
As you can see, all the properties of the tag, class or ID are inside the brackets. You can have it shortend too

<style>
body{background-color: red;}
.class{background: url(Insert_URL);}
#id{width: 400px; height: 100 px;}
</style>
That would be the exact same thing. It is just alot easier to have it like the first one.
Since there are alot of properties for CSS, I will just put a link for yall to go by
http://htmlhelp.com/reference/css/properties.html