SQL Server Transaction Rollback: does log shrink or grow?

When cancelling a transaction, be it e. g. via failure or manually when it runs too long, what is the effect on the transaction log and its size?

Do all the entries generated during and related to the transaction get deleted again (in both DB and LOG) or does the undo result in the same number of entries in the log, just undoing what was done before, growing the LOG file further?

Since deleting might be difficult in case of overlapping operations, I tend towards the latter, still I wonder and could not find out.