Bundler warnings: variable ... is undefined and used without a fallback

When upgrading from Bootstrap 4 to 5, a warning may be displayed, and the UI may break.

warn  variable --bs-offcanvas-width is undefined and used without a fallback

The solution is to disable the variables in the bundler (bloggify.js):

bundler: {
  cssExtensions: {
    cssnextVariables: false,
  }   
}