Nebular's CSS is not loaded from the start of the application

### Issue type

**I'm submitting a ...** (check one with "x")

* [x] bug report
* [ ] feature request

### Issue description

**Current behavior:**
When I want to place a spinner while the screen is loading, the spinner loads without the css or most of the time it doesn't even appear

**Expected behavior:**
The spinner should appear with every loaded css

**Steps to reproduce:**

1. Create a service to monitor route events
2. Place a spinner with an observable

**Related code:**

- https://stackblitz.com/edit/github-cfqkgp
- https://github-cfqkgp.stackblitz.io

### Other information:

**npm, node, OS, Browser**
```
Node: 12.6.0
Npm: 6.14.7
OS: Windows 10
Browser: Chrome
```

**Angular, Nebular**
```
Nebular: 6.2.1
Angular: 10.1.5
```