semi transparent navigation drawer toolbar

<android.support.v7.widget.Toolbar xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/my_awesome_toolbar"
    android:layout_height="wrap_content"
    android:layout_width="match_parent"
    android:minHeight="?attr/actionBarSize"
    app:theme="@style/BackArrow"
    android:background="?attr/colorPrimary">

    <TextView
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:textColor="@color/black"
        android:gravity="center"
        android:id="@+id/titletool"
        android:textSize="16sp"
        android:textStyle="bold"/>
</android.support.v7.widget.Toolbar>