Thanks so much for yesterday. I don't think I could have done anything without you.
Expressing deep gratitude
ありがとう is casual and used with friends, family, and people of lower status. ありがとうございます is the polite form for strangers, superiors, and formal situations. どうも can be added for emphasis. The word originally comes from 有り難い, meaning 'rare/difficult to have' - expressing that something is precious.