völlig vs vollstandig. what's the difference?

[mcpopeawesome]

Hello,

Is there a difference between these two? Do they not both mean the same thing which is: completely?

Thank you.

[kragi]

Völlig is an adverb. Vollständig can be an adverb or an adjective.

[Biomax]

I have actually found in the dictionary that both völlig and vollständig can be adverb or adjective.