What Eorindill wrote should work fine, I've tested it with webdev in firefox.
Just for ease, here's your entire CSS file with a little formatting so that its easier to read.

html, body, div, p, table, td, form, img, h1, h2, h3, h4, h5, h6, input, select {
font-family: Verdana,Tahoma,Segoe,sans-serif;
font-size: 10pt;
}

body{
color: #000;
background: #000 url('http://i78.photobucket.com/albums/j87/Lethalladies/LL-logo-2fromNeraNoBorderDark.gif') repeat;
background-attachment: fixed;
}

form {
padding: 3px;
border: none;
}

img {
border: none;
}

hr {
color: #0000000;
}

.TabBar {
margin: 0px;
padding: 0px;
}

.SelectedTab {
background-color: #000000;
color: #ffccff;
border: solid 1px #0000000;
border-color: #0000000;
text-align: center;
padding: 2px;
}

.UnSelectedTab {
background-color: #000000;
color: #ff00ff;
border: solid 1px #0000000;
text-align: center;
cursor: pointer;
padding: 2px;
}

.UnSelectedTabMo {
background-color: #000000;
color: #ffccff;
border: solid 1px #0000000;
border-color: #0000000;
cursor: pointer;
text-align: center;
padding: 2px;
}

.AltGridRow {
background-color: #000000;
color: #ff00ff;
}

.NormGridRow {
background-color: #000000;
color: #ff00ff;
}

.ContentBox {
background-color: #000000;
border: solid 1px #0000000;
}

.ContentBoxTitle {
padding: 5px;
background-color: #000000;
color: #ffccff;
}

.ContentBoxBody {
background-color: #000000;
color: #ff00ff;
padding-left: 5px;
padding-right: 5px;
padding-top: 5px;
padding-bottom: 5px;
}

.StateBar {
background-color: #000000;
color: #ff00ff;
text-align: center;
padding: 5px;
}

.ForumCategoryHeader {
background-color: #000000;
border-width: 1px 1px 1px 1px;
border-style: solid;
border-color: #0000000;
padding-left: 5px;
color: #ff00ff;
padding-right: 5px;
padding-top: 5px;
padding-bottom: 5px;
}

.ContentBoxTitleNoBackground {
color: #ffccff;
margin-top: 0px;
padding-top: 0px;
}

A:active {
color: #ff0099;
 text-decoration: none;
}

A:link {
color: #ff0099;
text-decoration: none;
}

A:hover {
color: #ff0099;
text-decoration: underline;
}

A:visited {
color: #cc99ff;
text-decoration: none;
}

.toolTipHeader {
color: lime;
font-weight: bold;
}

The styles inside the style sheet should only override the inline styles you have included in the stylesheet. This is what 'CSS' is...

Your browser looks at your CSS stylesheet first, and then it looks at embedded or inline styles.  If your CSS doesn't specify a style for a particular tag, then it looks to your inline styles and uses that.

The only instance where I could see this as a problem may be where guild portal has some sort of scripting that forces the browser not to look at inline styles somehow.

What section/css tags of your site is affected specifically?