einverstanden
agreed
Expresses agreement with a suggestion, opinion, or plan. You have the same opinion or accept something.
Bist du damit einverstanden, wenn wir uns morgen treffen?
Are you okay with it if we meet tomorrow?

agreed
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agreed
Expresses agreement with a suggestion, opinion, or plan. You have the same opinion or accept something.
Bist du damit einverstanden, wenn wir uns morgen treffen?
Are you okay with it if we meet tomorrow?

The word is made up of 'ein' and 'verstanden' (from 'verstehen' (to understand)). Figuratively, it describes that people have come to a common understanding.
Gut, dann sind wir uns ja einig und alle sind einverstanden.
Good, then we agree and everyone is on board.
When you agree, you are 'mit' something 'einverstanden' (in agreement with something). The preposition 'mit' always takes the dative.
Ich bin mit deinem Vorschlag voll und ganz einverstanden.
I fully agree with your suggestion.
'Einverstanden' (agreed) is almost always used predicatively, that is, after the noun with a verb like 'sein' (to be). Using it directly before a noun (attributively) is extremely rare and sounds unnatural.
Mein Chef ist mit dem Ergebnis einverstanden.
My boss is satisfied with the result.
To agree to an action, you use the construction 'damit einverstanden sein, dass ...' (to be okay with the fact that ...) or, less commonly, with an infinitive clause '..., ... zu tun' (... to do something).
Sie war damit einverstanden, dass wir das Projekt verschieben.
She was okay with us postponing the project.
against it / however
'dagegen' and 'einverstanden' are clear opposites when it comes to opinions or plans. Someone who is 'dagegen' rejects something or takes an opposing position. Someone who is 'einverstanden' agrees and accepts the suggestion. 'dagegen' often stands on its own after a plan or suggestion, while 'einverstanden' is often used with 'sein': 'Ich bin einverstanden' (I agree / I’m okay with it).

Nach kurzer Diskussion ist sie mit dem neuen Termin einverstanden.
After a short discussion, she agrees to the new appointment time.
Bei der Besprechung sind die Eltern gegen längere Bildschirmzeiten für die Kinder dagegen.
At the meeting, the parents are against longer screen time for the children.