The UK have left the EU on the 31 January 2020. There will now be a transition period until 31 December 2020. During the transition period there will be no changes in practice for citizens and businesses on both sides of the Channel.
As a Swedish citizens living in the UK, or moving to the UK during the transition period, you will, if you intend to stay after 2020, have to apply for settled status:
EU Settlement Scheme - you will find all information via this link
Telephone, Fridays 1.30-3pm, +44 20 7917 6470
For information about Swedish citizenship, see the Swedish Migration Agency’s website.
Moving to or living in Sweden, see The British government: Living in Sweden
You will also find useful information on Skatteverket's website.
During the transition period there will be no changes in practice for citizens. As a british citizen you will be able to travel to Sweden as before brexit and the same applies for Swedish citizens travelling to the UK.