Swern's Triangle sum

Consider the Triangle shown below. All of the angles are labeled and their measures are shown. At the top, all 3 of the angles are added up and we can see the sum.
Drag around the vertices of the triangle and change its shape. 1) What do you notice is special about the sum of the 3 angles? 2) Is there anything you can do to get the sum to change? 3) Based on what you see here, come up with a rule for the 3 interior angles in a triangle.