New to CSS/Web design needing help formatting my masterpage

<%@MasterLanguage="C#"AutoEventWireup="true"CodeFile="MasterPage.master.cs"Inherits="MasterPage" %>
<%@RegisterAssembly="AjaxControlToolkit"Namespace="AjaxControlToolkit"TagPrefix="cc1" %>
<!DOCTYPEhtmlPUBLIC"-//W3C//DTD XHTML 1.0 Transitional//EN""http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<htmlxmlns="http://www.w3.org/1999/xhtml">
<headrunat="server">
<title>Untitled Page</title>
<linkhref="StyleSheet.css"type="text/css"rel="stylesheet"/>
 
</head>
<bodybgcolor="white">
<formid="form1"runat="server">
<divid="header">
<divid="logo">
<imgsrc="logo1.gif"class="imgBorder"style="height: 147px"/></div>
<divid="HeaderAddress">
Address<br/>
Address<br/>
Address<br/>
Address<br/>
Address<br/>
Address<br/>
Address 
</div></div><divid="lowerheader"></div>
<br/>
<divid="sidebar"class="Borders">
<asp:TreeViewID="TreeView1"runat="server"DataSourceID="SiteMapDataSource1"Style="position: relative; left: 19px; top: 6px;"Height="298px"Width="150px"BackColor="Red"ForeColor="White">
<HoverNodeStyleForeColor="Black"/>
<SelectedNodeStyleForeColor="Blue"/>
</asp:TreeView>
&nbsp;&nbsp;
</div>
<asp:SiteMapDataSourceID="SiteMapDataSource1"runat="server"/>
</form>
</body>
</html>

body{
margin:25px25px025px;
padding:0;
background:white;
}
#header{
background: red;
height: 200px; /*Height of Header section*/
margin:20;
}
#lowerheader
{
background:black;
height:30px; 
}
#logo
{
float:left;
height: 150px; 
width: 150px; 

}
#sidebar
{
background: red;
width: 185px;
 
}
.Borders
{
border-bottom-color:Black;
border-left-color:Black;
border-right-color:Black;
border-top-color:Black;
border-bottom-style:solid;
border-left-style: solid;
border-right-style: solid;
border-top-style: solid;
}
 
#content
{
background:white 

}
.tl {background: url(TL_Red.gif)00no-repeat} 
.tr {background: url(TR_Red.gif)100%0no-repeat; padding:10px} 
#HeaderAddress/*Align Name & Address to the right*/
{

float:right;
text-align:right;
text-transform:uppercase;
vertical-align: middle;
color:white;
font-style:italic;
font-size:12pt;
font-weight:bolder;
margin:10;
}
.imgBorder/*Border for image*/
{
left: 2px; 
border-right: blackthinsolid;
border-top: blackthinsolid; 
border-left: blackthinsolid; 
border-bottom: blackthinsolid; 
position: relative;
top: 2px; 
height: 182px; 
}