一个非常基本的代码是：
只是一个简单的hello world，带有一些样式和居中对齐的文本。文本在预览中居中对齐，但在模拟器或真实的Android设备中不对齐。
下面是完整的代码：

package com.example.jetpackcomposetutorial

import android.os.Bundle
import androidx.activity.ComponentActivity
import androidx.activity.compose.setContent
import androidx.compose.foundation.layout.fillMaxSize
import androidx.compose.material3.MaterialTheme
import androidx.compose.material3.Surface
import androidx.compose.material3.Text
import androidx.compose.runtime.Composable
import androidx.compose.ui.Modifier
import androidx.compose.ui.graphics.Color
import androidx.compose.ui.text.font.FontStyle
import androidx.compose.ui.text.font.FontWeight
import androidx.compose.ui.text.style.TextAlign
import androidx.compose.ui.tooling.preview.Preview
import androidx.compose.ui.unit.sp
import com.example.jetpackcomposetutorial.ui.theme.JetpackComposeTutorialTheme

class MainActivity : ComponentActivity() {
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContent {
            SayHello()
        }
    }
}

@Preview(showSystemUi = true)
@Composable
fun SayHello(name:String = "World"){
    Text(
        text = "Hello $name",
        fontStyle = FontStyle.Italic,
        fontWeight = FontWeight.ExtraBold,
        color = Color.Red,
        textAlign = TextAlign.Center,
        fontSize = 30.sp
    )
}

1. Preview
2. Emulator
   这是一个bug还是我做错了什么？