NewPipe-app-android/app/src/main/res/drawable/popup_controls_bg.xml

<?xml version="1.0" encoding="utf-8"?>
<shape xmlns:android="http://schemas.android.com/apk/res/android">
    <gradient
        android:startColor="#a0000000"
        android:centerColor="#26000000"
        android:endColor="#00000000"
        android:angle="90"
        />
</shape>