Production build produces warning

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* [x] bug report
* [ ] feature request
* [ ] question about the decisions made in the repository

Because I cant use your template in a production build

### Issue description

**Current behavior:**

Run a production build: ng build --prod --aot
Produces a warning
**WARNING in Invalid background value at 37366:14. Ignoring.**
I have a work around without going through all the css to find why it wasnt combined properly.
ng build --prod --aot --extract-css=false

**Expected behavior:**

Run the production build without adding --extract-css flag

**Steps to reproduce:**

1. Clone repo
2. Install packages : npm install
3. Run the build: ng build --prod --aot

### Other information:

**npm, node, OS, Browser**
```
node --version -> v12.10.0

ng --version

_ _ ____ _ ___
/ \ _ __ __ _ _ _| | __ _ _ __ / ___| | |_ _|
/ △ \ | '_ \ / _` | | | | |/ _` | '__| | | | | | |
/ ___ \| | | | (_| | |_| | | (_| | | | |___| |___ | |
/_/ \_\_| |_|\__, |\__,_|_|\__,_|_| \____|_____|___|
|___/

Angular CLI: 8.3.3
Node: 12.10.0
OS: win32 x64
Angular:
...

Package Version
------------------------------------------------------
@angular-devkit/architect 0.803.3
@angular-devkit/core 8.3.3
@angular-devkit/schematics 8.3.3
@schematics/angular 8.3.3
@schematics/update 0.803.3
rxjs 6.4.0