[Suggestion] Improved readability in diffEditor and active tab

[fungilation]

First, thank you for your great theme! Best dark theme for VS Code and I've tried many.

A few readability issues irks me in using it though, so I fixed them with below. For your consideration, either in user settings or merging into Gatito:

  "workbench.colorCustomizations": {
    "diffEditor.insertedTextBackground": "#004a007f",
    "diffEditor.removedTextBackground": "#97000055",
    "diffEditor.insertedTextBorder": "#FFFFFF1c",
    "diffEditor.removedTextBorder": "#FFFFFF1c",
    "scrollbarSlider.activeBackground": "#FFFFFF64",
    "scrollbarSlider.background": "#ffffff42",
    "scrollbarSlider.hoverBackground": "#FFFFFF77",
    "tab.activeBorderTop": "#ffffff"
  },

Rationale

• diffEditor.* changes as such uses a dark red and green background color scheme, with only a faint outline on the inserted/removed bits, while those bits uses an alpha channel with as much contrast as I can make them to stand out from the unchanged bits within changed lines. Previously the whole changed line is the same color, relying only on prominent border around those bits which is confusing on where borders start and where they end on what are the actual bits that changed
• White tab.activeBorderTop to make what is the active tab easily glanceable (currently background of active tab is only slightly brighter than inactive tabs)
• scrollbarSlider.* to make scroll position also more easily glanceable