Holidays are not something that can be catched by STL decomposition. Instead you should use a model that enables you to include holiday dummies. One such model is Facebook's prophet, that is able to decompose the time-series to seasonal patterns, trend, include specific dummies, and allow for structural changes by detecting changepoints and using them as variables for piecewise regression.

Holidays are not something that can be handled by STL decomposition. Instead you should use a model that enables you to include holiday dummies. One such model is Facebook's prophet, that is able to decompose the time-series to seasonal patterns, trend, include specific dummies, and allow for structural changes by detecting change-points and using them as variables for piecewise regression.