Android Compose 如何去掉DropdownMenu的默认背景色？

Question

    val blue = Color(0xFF5851DB)
    val purple = Color(0xFF833AB4)
    val gradientBluePurple = listOf(blue, purple)    
    
    @Composable
    fun DropdownMenuDemo() {
        var expanded = remember { mutableStateOf(false) }
        Column(modifier = Modifier
            .fillMaxWidth()
            .background(Color.Green)) {
            IconButton(onClick = { expanded.value = true }) {
                Icon(imageVector = Icons.Default.MoreVert, contentDescription = null)
            }
            DropdownMenu(
                expanded = expanded.value,
                onDismissRequest = { expanded.value = false },
                modifier = Modifier
                    .fillMaxWidth()
                    .background(
                        brush = Brush.horizontalGradient(colors = gradientBluePurple),
                        shape = RoundedCornerShape(bottomStart = 24.dp, bottomEnd = 24.dp)
                    )
            ) {
                DropdownMenuItem(onClick = { }) {
                    Text("分享")
                }
                DropdownMenuItem(onClick = { }) {
                    Text("举报")
                }
                DropdownMenuItem(onClick = { }) {
                    Text("关注")
                }
            }
        }
    }