XML markup (layout problem)


Hello again,
I can not get the correct markup of the login page in two positions (landscape and portrait).
I want in both cases to split the screen into two layers of 50% each. The content of the first layer is centered (vertical-align: center), and the content of the second layer (vertical-align: top). Provided that it should be wrapped in ScrollView. At the moment I have only such a markup:

    <FlexboxLayout flexDirection="column" justifyContent="center">
        <StackLayout> <!-- first layout -->
        <StackLayout> <!-- second layout -->
            <StackLayout class="input-field">
                <TextField hint="login"></TextField>
            <StackLayout class="input-field">
                <TextField hint="passdrow"></TextField>
            <Button class="btn-submit" text="Enter"></Button>