Ionic React css background url -- schema-utils

As soon as I added css to style the background of an element with an image:

background: #164C77 url(../images/earth_bg.png) no-repeat 0 0;

I now receive the error ‘Failed to compile’:

Error: Cannot find module 'schema-utils'

I subsequently installed the npm module but nothing has changed. Is there a way I have to include this in my files (other than package.json) to make use of the url property of css?