Add and refactor tests for features of element "appbars" on a test-site

[annav00]

The class shouldn't contain elements specific to the test site. Appbar extends Toolbar hat is why it is necessary to close issue 4168 before starting this one.

Add and refactor tests for features of element "appbars" on a test-site:

• [ ] elevation (0-24)
• [ ] color(red/orange/green /yellow/blue/purple)
• [ ] outlined (y/n)
• [ ] flat (y/n)
• [ ] form (rounded, shaped)
• [ ] collapse (y/n)
• [ ] collapse-on-scroll (y/n)
• [ ] dense(y/n)
• [ ] short (y/n)
• [ ] elevate-on-scroll (y/n)
• [ ] hide-on-scroll (y/n)
• [ ] src (link)
• [ ] inverted-scroll (y/n)
• [ ] prominent (y/n)
• [ ] scroll-threshold (0-n)

Before taking this issue, make sure that the necessary elements are added to the test-site (issue 4169)