Environment

• Cross-platform modules: 6.2

Describe the bug
Setting the css property on page will apply styles globally when the page does not have a css file.

To Reproduce
Playground link: https://play.nativescript.org/?template=play-tsc&id=OvZEeJ

1. Click Navigate Leak
2. Click the button on the new page - it will set the page background
3. Go back -> the background on the start page is also set

Expected behavior
Use the same playground:

1. Click Navigate No Leak
2. Click the button on the new page - it will set the page background
3. Go back -> the initial page is not affected

Additional context
When a page has a CSS file it is always a style-host and has its own StyleScope created. When setting the CSS it is used and styles does not leak.
When a page has no CSS files - it uses the StyleScope from its parent to when setting CSS and it is applied to other pages in the same frame.