Prettier 3.6.2
Playground link

Input:

:root {
  --color-my-green: oklch(from rgb(255, 0, 0) l c +130);
}

Output:

:root {
  --color-my-green: oklch(from rgb(255, 0, 0) l c + 130);
}

Expected output:

:root {
  --color-my-green: oklch(from rgb(255, 0, 0) l c +130);
}

Why?

Adding a space between the + and the 130 changes the behaviour of the css. This is not a normal addition but putting the + there makes the 130 relative instead of absolute.