Cannot see the last few menu items in the sidebar

### Issue type

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

* [ x] bug report
* [ ] feature request

### Issue description

**Current behavior:**

I have a menu in the sidebar which has 25 items. The last few items are hidden from bottom and cannot see it with scrolling.

I added the following to fix the problem:
```
nb-menu {
margin-bottom: 80px;
}

```
**Expected behavior:**

Sidebar to display all the menu items

**Related Code:**
```

```

**Angular, Nebular**
Angular 8 and Nebular 4