Block cursor contrast with text is poor

This issue makes it difficult to use this theme with a Vim Plugin. edit: VSCode recently added this option as a workaround:

"workbench.colorCustomizations": {
  "editorCursor.foreground": "#fff000", // e.g highlight cusor color
  "editorCursor.background": "#000000" // e.g highlight text color
  },

However, it might be a good idea to modify the defaults so users don’t run into this issue.

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Done

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@silesky @kaosmos I improve it