public void setDrawerShadow(@DrawableRes int resId, @EdgeGravity int gravity) {
        setDrawerShadow(ContextCompat.getDrawable(getContext(), resId), gravity);
    }
Set a simple drawable used for the left or right shadow. The drawable provided must have a
nonzero intrinsic width. For API 21 and above, an elevation will be set on the drawer
instead of using the provided shadow drawable.

<p>Note that for better support for both left-to-right and right-to-left layout
directions, a drawable for RTL layout (in additional to the one in LTR layout) can be
defined with a resource qualifier "ldrtl" for API 17 and above with the gravity
{@link GravityCompat#START}. Alternatively, for API 23 and above, the drawable can
auto-mirrored such that the drawable will be mirrored in RTL layout.</p>

@param resId   Resource id of a shadow drawable to use at the edge of a drawer
@param gravity Which drawer the shadow should apply to
app/src/main/java/com/sunnyweather/android/ui/customerUIs/HomeDrawerLayout.java