! Undefined control sequence.
\tcb@startbox ...x }{\tcb@w@upper }\tcb@lua@color
{tcbcolupper}\kvtcb@fontup...
l.147 \begin{document}
The control sequence at the end of the top line
of your error message was never \def'ed. If you have
misspelled it (e.g., `\hobx'), type `I' and the correct
spelling (e.g., `I\hbox'). Otherwise just continue,
and I'll forget about whatever was undefined.
! Undefined control sequence.
\tcb@startbox ...x }{\tcb@w@upper }\tcb@lua@color
{tcbcolupper}\kvtcb@fontup...