It appears as if there is a bug in assets/scss/pro_lightbox.scss.

All instances of:

url(../img/lightbox/default-skin.png)

Should be replaced with --

url(#{$image-path}lightbox/default-skin.png)

This would allow me to import the scss file from my project's styles.scss providing the means to inject custom themes without having to modify the node package. IMO, modifying the node package should not be considered a viable solution to custom theming.

$fa-font-path: '../node_modules/font-awesome/fonts/';
$roboto-font-path: '../node_modules/ng-uikit-pro-standard/assets/font/roboto/';
$image-path: '../node_modules/ng-uikit-pro-standard/assets/img/';
// Font Awesome
@import '~font-awesome/scss/font-awesome';
// Bootstrap
@import '~ng-uikit-pro-standard/assets/scss/bootstrap/bootstrap.scss';
// Load custom themes here
@import 'assets/scss/themes';
// MDBootstrap
@import '~ng-uikit-pro-standard/assets/scss/mdb';