Improve the user interface

[Aikatsui]

Is your feature request related to a problem? Please describe.
The extension have a good name and an eye-catching nice logo (the leaf especially) but there are a few issues with the user interface.

1. It's okay to have a big window to display everything at once, but make the most of the space.

Example:

2. Use a good font. Current font seems to occupy more space than necessary.
3. Fix the non-visible contents.

4. Introduce dark theme.
5. In the future, if there are many items to display, you could use columns like this to present additional content, so users won’t need to switch to other windows.