code: @Nullable
      public static Drawable getActionBarBackground(Context context) {
          int[] attrs = {android.R.attr.actionBarStyle};
          TypedArray a = context.obtainStyledAttributes(attrs);
          int id = a.getResourceId(0, 0);
          a.recycle();
          if (id > 0) {
              attrs[0] = android.R.attr.background;
              a = context.obtainStyledAttributes(id, attrs);
              Drawable background = a.getDrawable(0);
              a.recycle();
              return background;
          }
          return null;
      }
docs: Get the ActionBar background in the Context's theme.
  
  @return null if a background is not defined