Unable to fix element in place on mobile - html

Question

I've developed a web-application. Unfortunately, i met with some problem in terms of positioning.
As you can see from the image below, the mobile keyboard of my samsung s4 on google chrome caused my element from shifting beyond my header.
However, when i tested it on iPhone 4 with safari, this doesn't happen. Unfortunately, when i tested it on iPhone 4 with google chrome, the same problem persist.
This is how my html of my login page looks like
<div id="loginpage">
<table id="loginpage1" width="100%">
<tr>
<td>
<h2>Login</h2>
<br />
</td>
</tr>
<tr>
<td>
<b> Username : </b> <asp:TextBox ID="txtUsername" runat="server"></asp:TextBox>
<br />
<br />
</td>
</tr>
<tr>
<td>
<b> Password : </b> <asp:TextBox ID="txtPassword" runat="server" TextMode="Password" ></asp:TextBox>
<br />
<br />
</td>
</tr>
</table>
<table id="loginpage2" width="50%" align="center">
<tr>
<td align="right">
<b>Account Type :</b>
</td>
<td>
<asp:RadioButton ID="rbMember" runat="server" GroupName="rbGroup1" Text="Member" />
</td>
<td>
<asp:RadioButton ID="rbPolice" runat="server" GroupName="rbGroup1" Text="Officer" />
</td>
<td>
<asp:RadioButton ID="rbAdmin" runat="server" GroupName="rbGroup1" Text="Admin" />
</td>
<td>
<asp:RadioButton ID="rbSuperior" runat="server" GroupName="rbGroup1" Text="Superior" />
</td>
<td>
<asp:RadioButton ID="rbPoliceStaff" runat="server" GroupName="rbGroup1" Text="PoliceStaff" />
</td>
</tr>
<tr>
<td colspan="6" >
<b><asp:Label ID="lblMessage" runat="server" ></asp:Label></b>
<br />
<br />
</td>
</tr>
<tr>
<td colspan="6">
<asp:Button ID="btnLogin" runat="server" Text="Login" OnClick="btnLogin_Click" />
<br />
<br />
</td>
</tr>
<tr>
<td colspan="6">
<asp:LinkButton ID="lbtnMemberRegister" runat="server" OnClick="lbtnMemberRegister_Click">Register</asp:LinkButton>
</td>
</tr>
</table>
</div>
Here's my css
#loginpage
{
position:absolute;
margin-top:-15%;
overflow:hidden;
}
I used overflow:auto as well but it still the same. I attempted to change my position to relative but it doesn't work as well. I've added the margin-top:-15%; so as to align my login just slightly below my header without the mobile keyboard. But with the keyboard, it would look like the image i posted above. Therefore, i need to fix my element in it's original position.
Does anyone have any idea on how to solve this problem?