customized login style

### Issue type

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

* [x] bug report
* [ ] feature request

### Issue description

**Current behavior:**

I am customizing Login page by following document custom-auth-components (https://akveo.github.io/nebular/docs/auth/custom-auth-components#custom-auth-components, https://github.com/akveo/nebular/blob/master/src/playground/without-layout/smart-home/auth/login/login.component.html).
but I facing issue
1. If 'nb-alert' is an Angular component, then verify that it is part of this module.
2. If 'nb-alert' is a Web Component then add 'CUSTOM_ELEMENTS_SCHEMA' to the '@NgModule.schemas' of this component to suppress this message.

2

**Expected behavior:**

**Steps to reproduce:**

**Related code:**

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### Other information:

**npm, node, OS, Browser**
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**Angular, Nebular**
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