Android

• Add `launch_bg.png` and `launch_image.png` to

+ android/app/src/main/res/drawable-mdpi
+ android/app/src/main/res/drawable-xhdpi
+ android/app/src/main/res/drawable-xxhdpi

• Update `android/app/src/main/res/drawable/launch_background.xml`

<?xml version="1.0" encoding="utf-8"?>
<!-- Modify this file to customize your launch splash screen -->
<layer-list xmlns:android="http://schemas.android.com/apk/res/android">
    <item android:drawable="@android:color/white" />

    <!-- You can insert your own image assets here -->
    <item>
        <bitmap
            android:gravity="fill_horizontal|fill_vertical"
            android:src="@drawable/launch_bg" />
    </item>
    <item>
        <bitmap
            android:gravity="center"
            android:src="@drawable/launch_image" />
    </item>
</layer-list>

iOS

• Add `LaunchBackground.imageset` and `LaunchImage.imageset` to `ios/Runner/Assets.xcassets`
• Open `ios/Runner.xcworkspace`
• Select `Runner/Runner/LaunchScreen.storyboard`

+ Expand View Controller Scene -> View Controller -> View
+ Add object -> Search ImageView -> Drag ImageView object to View (front of LaunchImage) 
-> Select Attributes inspector -> Custom Image to LaunchBackground 
-> Change View Content Mode to Scale To Fill -> Add 0, 0, 0, 0 as constrains 
-> Save