Update formatting for Mac

As a user of the Multi-Dielectric Energy Band Diagram Program, I want to have a good experience so I will keep using it.

**Acceptance Criteria:**

- [x] Given I have downloaded the program, when I open it, the splash screen shows up in the middle of my screen.

Given I have downloaded the program, when the program is running:
- [x] All the text is visible (not cut off or replaced with '...')
- [x] The text is easy to read.
- [x] There is more border space, so the text isn't going all the way to the left edge.

No files or tests are named. Start by running the Java program on a Mac and inspect the splash screen and main interface; done means the splash screen is centered, text is fully visible and readable, and the layout has more left-side border space.

Scritto dal modello di indicizzazione a partire dal testo della issue.