MainActivity.kt

@ExperimentalAnimationApi
@Composable
fun Home() {
    val colorsArray = arrayOf(Purple, Blue, Red)
    var particleColor by remember { mutableStateOf(Color.White) }
    /* ... */
    
    Scaffold(
        topBar = {
            Box {
                Particle(
                    modifier = Modifier
                        .align(Alignment.BottomCenter),
                    color = particleColor
                )
                TopAppBar(
                    /* ... */
                    actions = {
                        IconButton(onClick = {
                            particleColor = colorsArray.random()
                        }) {
                            Icon(Icons.Filled.AddCircle, contentDescription = null)
                        }
                    },
                    /* ... */
                )
            }
        }
    ) { /* ... */ }
}