Merry Christmas! Can you solve the puzzle and find the hidden theme?

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Across
  1. 4. Former neighbor
  2. 6. Nickname for Los Angeles
  3. 10. Commitments to do or not do something
  4. 11. Imaginary law enforcement
  5. 13. Luminous sources
  6. 15. Disney song from Frozen
  7. 16. Hot part of a candle
Down
  1. 1. Whenever
  2. 2. Resident of the Golden State
  3. 3. Informal language or expressions
  4. 5. _____ Kingdom
  5. 7. At this moment in time
  6. 8. Give up
  7. 9. Welcoming gesture
  8. 12. Captured image with a camera
  9. 14. Loyally