jetpack compose - Box gravity

MainActivity.kt

package com.cfsuman.jetpackcompose

import androidx.appcompat.app.AppCompatActivity
import android.os.Bundle
import androidx.activity.compose.setContent
import androidx.compose.foundation.background
import androidx.compose.foundation.layout.*
import androidx.compose.foundation.shape.RoundedCornerShape
import androidx.compose.material.*
import androidx.compose.runtime.*
import androidx.compose.ui.Alignment
import androidx.compose.ui.Modifier
import androidx.compose.ui.draw.clip
import androidx.compose.ui.graphics.Color
import androidx.compose.ui.tooling.preview.Preview
import androidx.compose.ui.unit.dp

class MainActivity : AppCompatActivity() {
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)

        setContent {
            GetScaffold()
        }
    }


    @Composable
    fun GetScaffold(){
        Scaffold(
            topBar = {TopAppBar(
                title = {Text(
                    "Compose - Box Gravity",
                    color = Color.White)},
                backgroundColor = Color(0xFF58427C)) },
            content = {MainContent()},
            backgroundColor = Color(0xFFEDEAE0)
        )
    }


    @Composable
    fun MainContent(){
        Column(
            modifier = Modifier
                .fillMaxSize(),
            verticalArrangement = Arrangement.SpaceEvenly,
            horizontalAlignment = Alignment.CenterHorizontally
        ){
            Box(
                Modifier
                    .padding(12.dp)
                    .fillMaxWidth()
                    .height(150.dp)
                    .clip(RoundedCornerShape(12.dp))
                    .background(Color(0xFFB2FFFF))
                    .padding(12.dp),
                contentAlignment = Alignment.Center
            ){
                Text(
                    text = "Gravity Center",
                    style = MaterialTheme.typography.caption
                )
            }

            Box(
                Modifier
                    .padding(12.dp)
                    .fillMaxWidth()
                    .height(150.dp)
                    .clip(RoundedCornerShape(12.dp))
                    .background(Color(0xFFB2EC5D))
                    .padding(12.dp),
                contentAlignment = Alignment.CenterStart
            ){
                Text(
                    text = "Gravity Center Vertically",
                    style = MaterialTheme.typography.caption
                )
            }

            Box(
                Modifier
                    .padding(12.dp)
                    .fillMaxWidth()
                    .height(150.dp)
                    .clip(RoundedCornerShape(12.dp))
                    .background(Color(0xFFD6CADD))
                    .padding(12.dp),
                contentAlignment = Alignment.TopCenter
            ){
                Text(
                    text = "Gravity Center Horizontally",
                    style = MaterialTheme.typography.caption
                )
            }
        }
    }


    @Preview
    @Composable
    fun ComposablePreview(){
        //GetScaffold()
    }
}