Implemented additional animation for when the calculator button was clicked

[TechEvolvace]

New changes to the animation

• The shadow under the calculator button that was clicked on will glow yellow for 0.1s, which is long enough for the user to notice that the calculator button was successfully clicked and brief enough to ensure for additional clicks on that same button.

[TechEvolvace]

This fulfills a criteria for the accessibility features issue of this project: to implement some animation that involves the calculator button's shadow to glow yellow to indicate a successful click on any of the calculator buttons!