How to set entry control over an image?

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C#

Xamarin

Hi,
I want to set an Entry (input text in Android/iOS) over an image that plays an input box role. I tried this XAML code but I couldn't set its correct position over the first rectangle (image):
https://s4.uupload.ir/files/1_hepn.png[^]

What I have tried:

<Grid>
        <Grid.RowDefinitions>
            <RowDefinition Height="300"/>
            <RowDefinition Height="300"/>
            <RowDefinition Height="Auto"/>
            <RowDefinition Height="Auto"/>
            <RowDefinition Height="Auto"/>
        </Grid.RowDefinitions>
        <Image Source="Rectangle2.png" Grid.Row="0" Margin="2,10,0,0"/>
        <Image Source="Rectangle2.png" Grid.Row="1" Margin="2,-300,0,0" />
        <Grid Grid.Row="0">
            <Grid.ColumnDefinitions>
                <ColumnDefinition Width="350"/>
            </Grid.ColumnDefinitions>
            <Grid.RowDefinitions>
                <RowDefinition Height="60"/>
            </Grid.RowDefinitions>
            <Entry  Grid.Row="0" Margin="25,0,0,0" Placeholder="User Name:" PlaceholderColor="DimGray" MaxLength="30"  ClearButtonVisibility="WhileEditing" TextColor="Black" />
        </Grid>

    </Grid>