Set GridView Header Text Center aligned using CSS in ASP.Net

Below is my gridview, which heading is not coming in center

<asp:GridView ID="gvv" runat="server" AutoGenerateColumns="false" Style="margin-left: 560px" GridLines="None"
    CssClass="grid" HeaderStyle-CssClass="header" RowStyle-CssClass="row" AlternatingRowStyle-CssClass="row" Width="560px">
    <Columns>
        <asp:TemplateField HeaderText="ID">
            <ItemTemplate>
                <asp:Label ID="Code" runat="server" Text='<%#Bind("Code")%>'></asp:Label>
            </ItemTemplate>
        </asp:TemplateField>
        <asp:TemplateField HeaderText="Name">
            <ItemTemplate>
                <asp:Label ID="Item_Name" runat="server" Text='<%#Bind("Item_Name")%>'></asp:Label>
            </ItemTemplate>
        </asp:TemplateField>
    </Columns>
</asp:GridView>
<style type="text/css">
    .grid {
        font: 16px Arial, Sans-Serif;
    }

    .grid td, .grid th {
        padding: 10px;
    }

    .header {
        text-align: center;
        color: white;
        background-color: blue;
    }

    .row td {
        border-bottom: solid 1px blue;
    }

    .alternating {
        background-color: #eeeeee;
    }

    .alternating td {
        border-bottom: solid 1px blue;
    }
</style>