Bug with broken css styles after refreshing page

### Issue type

**I'm submitting a bug report after installing ngx-admin and deploying it in production mode** (check one with "x")

* [x] bug report
* [ ] feature request

### Issue description

**Current behavior:**
Sometimes, after reloading or refreshing the page, broken styles are displayed for a second, for example: svg-icons at full screen size, then everything goes fine

**Expected behavior:**
Not to see broken styles after reloading or refreshing the page at all

**Steps to reproduce:**
Install ngx-admin following this guide (https://akveo.github.io/ngx-admin/docs/getting-started/installation-guidelines#install-ngxadmin).
Then run this command 'npm run build:prod'. Get the dist folder and put it under your web server. Then deploy server and try to refresh or reload pages multiple times.

**Related code:**
How bug looks like:


### Other information:

**npm, node, OS, Browser**
```

Node: 14.18.1
Package Manager: npm 7.24.2
OS: linux x64 ubuntu 20.04

Browser: Chrome 96, Opera, Edge

**Angular, Nebular**
Angular 12
Nebular 8