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.

未指定文件或测试。首先在 Mac 上运行 Java 程序，并检查启动画面和主界面；当启动画面居中、文本完全可见且易于阅读，并且布局左侧有更多边框空间时，即表示完成。

由索引模型根据 Issue 内容生成。