How to style DetailsView control using CSS in ASP.Net

Try This

.Grid { border: solid 1px #FFFFFF; }
.Grid td
{
border: solid 1px #FFFFFF;
margin: 1px 1px 1px 1px;
padding: 1px 1px 1px 1px;
text-align: center;
}
.GridHeader
{
font-weight: bold;
background-color: #8b8dbb;
}
.GridItem
{
background-color: #e6e6e6;
}

.GridAltItem
{
background-color: white;
}

 <asp:DetailsView ID="DetailsView1" CssClass=”Grid”>
 </asp:DetailsView>

 or

Refer

http://www.asp.net/cssadapters/detailsview.aspx

Try This

<asp:DetailsView ID="DetailsView1" runat="server" DataSourceID="SqlDataSource1" AutoGenerateRows="false" OnDataBound="DetailsView1_DataBound">
        <Fields>
          <asp:TemplateField>
            <ItemTemplate>
              <table id="Table1" runat="server" width="400" cellpadding="0" cellspacing="0">
                <tr height="50">
                  <td width="33%" align="center">Name:<asp:Label runat="server" ID="l1" Text='<%# Eval("Name") %>'></asp:Label></td>
                  <td width="33%" align="center"></td>
                  <td width="33%" align="center">Phone:<asp:Label runat="server" ID="l2" Text='<%# Eval("Number") %>'></asp:Label></td>
                   </tr> 
                   <tr height="50">
                  <td width="33%" align="center">Description:<asp:Label runat="server" ID="Label1" Text='<%# Eval("Description") %>'></asp:Label></td>
                  <td width="33%" align="center"></td>
                  <td width="33%" align="center">Amount:<asp:Label runat="server" ID="Label2" Text='<%# Eval("Amount") %>'></asp:Label></td>
                   </tr>
              </table>
            </ItemTemplate>
          </asp:TemplateField>
        </Fields>
</asp:DetailsView>

DetailsView Cannot be look like what you are thinking Use ListView or GridVirew Instead. Here i have shown you how to apply the curves to table.

HTML:

<div class="rounded_corners" style="width: 300px">
            <asp:DetailsView ID="DetailsView1" CssClass="table table-curved" AllowPaging="True"
                HeaderStyle-BackColor="#3AC0F2" HeaderStyle-ForeColor="White" RowStyle-BackColor="#A1DCF2"
                AlternatingRowStyle-BackColor="White" RowStyle-ForeColor="#3A3A3A" Width="300"
                OnPageIndexChanging="DetailsView1_OnPageIndexChanging" runat="server">
                <Fields>
                    <asp:BoundField DataField="Name" HeaderText="Name" />
                    <asp:BoundField DataField="Company" HeaderText="Company" />
                    <asp:BoundField DataField="Qual" HeaderText="Qual" />
                    <asp:BoundField DataField="PersNo" HeaderText="PersNo" />
                </Fields>
            </asp:DetailsView>
        </div>

STYLE:

<style type="text/css">
        .rounded_corners
        {
            border: 1px solid #A1DCF2;
            -webkit-border-radius: 8px;
            -moz-border-radius: 8px;
            border-radius: 8px;
            overflow: hidden;
        }
        .rounded_corners td, .rounded_corners th
        {
            border: 1px solid #A1DCF2;
            font-family: Arial;
            font-size: 10pt;
            text-align: center;
        }
        .rounded_corners table table td
        {
            border-style: none;
        }
    </style>

C#:

protected void Page_Load(object sender, EventArgs e)
    {
        if (!this.IsPostBack)
        {
            this.PopulateGrid();
        }
    }

    private void PopulateGrid()
    {
        string constr = ConfigurationManager.ConnectionStrings["constr"].ConnectionString;
        string sqlStatment = "SELECT * FROM pers";
        using (SqlConnection con = new SqlConnection(constr))
        {
            using (SqlCommand cmd = new SqlCommand(sqlStatment, con))
            {
                using (SqlDataAdapter da = new SqlDataAdapter(cmd))
                {
                    DataSet ds = new DataSet();
                    da.Fill(ds);
                    this.GridView1.DataSource = ds;
                    this.GridView1.DataBind();
                    this.DetailsView1.DataSource = ds;
                    this.DetailsView1.DataBind();
                }
            }
        }
    }

    protected void DetailsView1_OnPageIndexChanging(object sender, DetailsViewPageEventArgs e)
    {
        this.DetailsView1.PageIndex = e.NewPageIndex;
        PopulateGrid();
    }

OUTPUT: