LONDON — Now comes the harder part.

On Sunday, the 27 other members of the European Union gave the green light to Prime Minister Theresa May’s deal to seal Britain’s divorce from the bloc.

But she still has huge hurdles to overcome.

What’s next?

• Mrs. May will take the pact to the British Parliament: The prime minister must win the support of lawmakers who agree with rivals like Boris Johnson and Jacob Rees-Mogg, who had given her Brexit plan scathing reviews, and some members of the opposition Labour Party, which has promised to vote against the deal.

• Lawmakers will vote: A vote is expected before Christmas. Foreign Secretary Jeremy Hunt said on Sunday that “the arithmetic” to get the votes was looking “challenging.” Mrs. May took her case to the people, writing an open letter to the nation in which she argued that the deal was “one that works for our whole country and all of our people, whether you voted ‘Leave’ or ‘Remain.’”

• Transition would follow approval. Both the House of Commons and the European Parliament must sign off on the deal. If that happens, Britain would be on course to leave the bloc on March 29, with a transition period until December 2020.