fraction in fillMaxHeight inside a column not work(android jetpack compose)

I have a column with two buttons. at first I used maxSize for my Column and i set the vertical arrangement of my buttons to the bottom as you see in this picture. but I wanted to raise the buttons between the center and bottom of screen(about 78% of the screen size from the top see this pic) so that it would be responsive in every screen. this is my approch :

 Column(
    modifier = Modifier
        .fillMaxWidth()
        .fillMaxHeight(0.78f),
    horizontalAlignment = Alignment.CenterHorizontally,
    verticalArrangement = Arrangement.Bottom

) {
    Button(
        modifier = Modifier.fillMaxWidth(0.7f),
        onClick = {}) {

        Text(text = "Sign Up")
    }

    Button(
        modifier = Modifier.fillMaxWidth(0.7f),
        colors = ButtonDefaults.buttonColors(containerColor = Color.White),
        onClick = {}) {

        Text(
            text = "Sign In",
            color = Brown
        )
    }
}

but the problem is that it remained the same and buttons are in the bottom as well. do you have any opinion to make what I want?

The explanation for the behavior you observed:

If you use a Surface, the first child Composable will always have the same minimum size as the Surface. This was a decision intentionally made by the Android Development Team:

Surface is not really a layout. [...] So we come up with propagateMinConstraints=true idea, now the content inside Surface has to fill the min size applied on Surface.

There are two solutions:

A) Set the Surface to the exact size that you need by removing the Modifier.fillMaxSize()

B) Introduce an intermediate Composable, for example, a Column like this:

Surface(
    modifier = Modifier.fillMaxSize()
) {

    Column(
        modifier = Modifier.fillMaxSize()
    ) {

        Column(
            modifier = Modifier
                .fillMaxWidth()
                .fillMaxHeight(0.78f),  // should work now
            horizontalAlignment = Alignment.CenterHorizontally,
            verticalArrangement = Arrangement.Bottom
        ) {
            // ...
        }
    }
}

See also this stackoverflow question that goes more into depth.