message: Small typo fix in Theme docs
diff: @@ -15,7 +15,7 @@ completely new themes.
  The easiest way to create a new theme is to use the `createTheme` function
  exported by the
  [@backstage/theme](https://www.npmjs.com/package/@backstage/theme) package. You
  -can use it to override so basic parameters of the default theme such as the
  +can use it to override some basic parameters of the default theme such as the
  color palette and font.
  For example, you can create a new theme based on the default light theme like
  