Finsler-Hadwiger Action!!!

In the applet below, simply slide the slider very slowly and enjoy the phenomena you witness. After doing so, feel free to adjust the green and yellow sliders to change the sizes of the green and yellow squares, respectively. You can also change the locations of any of the white points. Interact with this applet for a few minutes. Then answer the questions that follow.

Write the phenomena you've witnessed several times as a conditional ("if-then") statement.

Can you use coordinate geometry to formally prove what this applet informally illustrates? (For starters, why not let the common vertex be (0,0) and go from there?)