Let’s define this clearly:

To elaborate on what that means…well, a trope can be anything as it encompasses a lot of things. One element can even embody multiple tropes and even groups of tropes can collectively make up one trope.
The majority of tropes are basically unimportant and not noteworthy…such as ‘brown-colored doors’.
Yep, this is pretty simple. A sub-category of ‘tropes’ is the Cliché.