from https://www.ibm.com/support/knowledgecenter/SSQNUZ_1.2.1/com.ibm.icpdata.doc/dsx/markd-jupyter.html
Blue boxes (alert-info)
Tip: Use blue boxes (alert-info) for tips and notes.
If it’s a note, you don’t have to include the word “Note”.
Yellow boxes (alert-warning)
Example: Use yellow boxes for examples that are not
inside code cells, or use for mathematical formulas if needed.
Green boxes (alert-success)
Up to you: Use green boxes sparingly, and only for some specific
purpose that the other boxes can't cover. For example, if you have a lot
of related content to link to, maybe you decide to use green boxes for
related links from each section of a notebook.
Red boxes (alert-danger)
Just don't: In general, avoid the red boxes. These should only be
used for actions that might cause data loss or another major issue.