[NTG-context] Piecewise margin line

Hello, I want to setup some fancy theorem style for my math notes. For this I want to have a colored margin line next to my theorems. It should look like this: https://i.ibb.co/F6L59pD/idea.png The line should stretch over the whole theorem, not just the first line. (But the latter would be a beginning, though.) Important to note is that the line should be *on the margin*, not in the text. So do you have an idea on how I could do that? I would greatly appreciate your answer. Thank you! Best regards, Johann