Added background and border for Errors, Warnings, and Hints

[Suhaybu]

The change

Backgrounds for Errors, Warnings and Hints now share the same color with elevated_surface.background. The border's of these hints now use a darker shade of their respective colors.

Visual Preview of the changes

Error popup

Warning popup

Hint popup

Test it yourself

To test the proposed changes before it's merged, add thiS to your Zed's settings.json

{
  "experimental.theme_overrides": {
    "error.background": "#1e2227",
    "error.border": "#a03237",
    "warning.background": "#1e2227",
    "warning.border": "#89734d",
    "hint.background": "#1e2227",
    "hint.border": "#013b64"
  }
}