1. 新增CSS樣式: Style style = new Style();

                       style.ForeColor = System.Drawing.Color.Navy;

                       style.BackColor = System.Drawing.Color.LightGray;

                       this.Header.StyleSheet.CreateStyleRule(style, null, "body");

2. 連結外部的CSS樣式表: HtmlLink link = new HtmlLink();

                                   link.Attributes.Add("type", "text/css");

                                   link.Attributes.Add("rel", "stylesheet");

                                   link.Attributes.Add("href", "~/newstyle.css");

                                   this.Header.Controls.Add(link);

方法3   aa.aspx.cs   public   string   m_StyleSrc   =   string.Empty; //公共變數  ,樣式檔案路徑       

                              private   void   Page_Load(object   sender,   System.EventArgs   e)     {             

                               m_StyleSrc   =  "../xxx.css";  //頁面載入時賦值      }    

                               }          

           aa.aspx      <LINK   href="<%=m_StyleSrc%>"   type="text/css"   rel="stylesheet">

方法4 下面這個方法沒試過,不知是否能用   

                 protected void Page_Onload(object sender, EventArgs e)     {

                                          Page.StyleSheetTheme = "../css/infomore.css"; 

                                         }

方法5   頁面：

                   <link   href=""   rel="stylesheet"   type="text/css"     id="css"   runat="server"/>  

          後臺  

                   this.css.Href   =   "css檔案路徑";