调试时的奇怪问题

说明一下，从iis浏览的话，不会出现一下情况。CSS：.InputText
{
border: 1px solid #ddd;
background: #fff url(../resource/image/input-shaddow.gif) no-repeat left top;
font: 11px Arial, Helvetica, sans-serif;
color: #646464;
padding: 5px 7px; 
float: left;
margin: 0 10px 0 0;
}
页面   <div id="wrapper" style="vertical-align: middle; text-align: center">
            <div id="main" style="text-align: left">
                <h3>
                    System Login</h3>
                <fieldset>
                    <dl>
                        <dt>ID:</dt>
                        <dd>
                            <asp:TextBox ID="tbid" runat="server" CssClass="InputText"></asp:TextBox>
                        </dd>
                    </dl>
                    <dl>
                        <dt>Password:</dt>
                        <dd>
                            <asp:TextBox ID="tbpwd" runat="server" CssClass="InputText1" TextMode="Password"></asp:TextBox>
                        </dd>
                    </dl>
                    <p>
                        <span>Valid Code:</span>
                        <asp:TextBox ID="tbvcd" runat="server" ></asp:TextBox>
                    </p>
                   
                        <img id="imgverify" alt="点击刷新验证码" style="cursor: pointer; text-align: center" onclick="getnewcode('imgverify')"
                            title="看不清换一张" />
                    </p> 
                     <p>
                        <asp:Button ID="btnsignin" runat="server" Text="sign in" CssClass="button-submit"
                            OnClick="btnsignin_Click" />
                        <asp:Button ID="btnclear" runat="server" Text="clear" CssClass="button-submit" OnClientClick="clear()" />
                    </p> 
 
                </fieldset>
            </div>
        </div>
handler /// <summary>
    /// $codebehindclassname$ 的摘要说明
    /// </summary>
    [WebService(Namespace = "http://tempuri.org/")]
    [WebServiceBinding(ConformsTo = WsiProfiles.BasicProfile1_1)]
    public class ValidCodeHandler : IHttpHandler, IRequiresSessionState
    {        int intLength = 5;               //长度
        string strIdentify = "Identify"; //随机字串存储键值，以便存储到Session中        #region IHttpHandler 成员        /// <summary>
        /// 实例可再次使用
        /// </summary>
        public bool IsReusable
        {
            get { return true; }
        }        /// <summary>
        /// 
        /// </summary>
        /// <param name="context"></param>
        public void ProcessRequest(HttpContext context)
        {
            //设置输出流图片格式
            context.Response.ContentType = "image/gif";            Bitmap b = new Bitmap(200, 60);
            Graphics g = Graphics.FromImage(b);
            g.FillRectangle(new SolidBrush(Color.YellowGreen), 0, 0, 200, 60);
            Font font = new Font(FontFamily.GenericSerif, 48, FontStyle.Bold, GraphicsUnit.Pixel);
            Random r = new Random();            //合法随机显示字符列表
            string strLetters = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890";
            StringBuilder s = new StringBuilder();            //将随机生成的字符串绘制到图片上
            for (int i = 0; i < intLength; i++)
            {
                s.Append(strLetters.Substring(r.Next(0, strLetters.Length - 1), 1));
                g.DrawString(s[s.Length - 1].ToString(), font, new SolidBrush(Color.Blue), i * 38, r.Next(0, 15));
            }            //生成干扰线条
            Pen pen = new Pen(new SolidBrush(Color.Blue), 2);
            for (int i = 0; i < 10; i++)
            {
                g.DrawLine(pen, new Point(r.Next(0, 199), r.Next(0, 59)), new Point(r.Next(0, 199), r.Next(0, 59)));
            }
            b.Save(context.Response.OutputStream, ImageFormat.Gif);            //不区分大小写
            context.Session[strIdentify] = s.ToString().ToLower(); //先保存在Session中，验证与用户输入是否一致
            context.Response.End();
        }        #endregion
    }
在debug时，页面上所有的控件的背景都变成了验证码