菊池 追記

app/src/main/java/com/example/oplogy/MainActivity.java

@@ -3,6 +3,7 @@ package com.example.oplogy;
 import androidx.appcompat.app.AppCompatActivity;
 
 import android.os.Bundle;
+import android.widget.TextView;
 
 public class MainActivity extends AppCompatActivity {
 
@@ -10,5 +11,7 @@ public class MainActivity extends AppCompatActivity {
     protected void onCreate(Bundle savedInstanceState) {
         super.onCreate(savedInstanceState);
         setContentView(R.layout.activity_main);
+
+        TextView textMain = findViewById(R.id.TextMain);
     }
 }

app/src/main/res/layout/activity_main.xml

@@ -13,17 +13,20 @@
         android:layout_height="wrap_content"/>
 
     <TextView
+        android:id="@+id/TextMain"
+        android:textColor="@color/material_on_background_disabled"
         android:layout_width="wrap_content"
         android:layout_height="wrap_content"
+        android:layout_marginTop="100dp"
         android:text="PracticeTeam"
         android:layout_gravity="center"
         android:textSize="50dp"/>
     <Button
-        android:layout_marginTop=""
+        android:layout_marginTop="300dp"
         android:layout_width="wrap_content"
         android:layout_height="wrap_content"
         android:text="開始"
-        android:textSize="20"
+        android:textSize="50dp"
         android:layout_gravity="center"
         />