Notices rendered as blockquotes

As described in learn.getgrav.org:
"Notices:
We have four notice styles and they extend the standard markdown syntax for block quotes. Basically levels of 3 block quote or greater produce notices in 4 colors"

But if I try to insert 3 or more block quote the intended colored notices are shown as 3 or more vertical lines?
I'm using agency theme...?

Yah, basically this is a CSS thing, and the comment about the notice styles extending block quotes is valid for Antimatter theme only.

You can probably take the styling for them from Antimatter and copy them in to the Agency CSS or custom.css of Agency theme.