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Sydney Sweeney just leveled up to 28 -- and her birthday blowout was outta this world, with celebs galore and her new flame Scooter Braun in full party mode.

The actress completely took over at her 'Planet Syd' bash at L.A.’s Vibiana on Sunday night ... wearing the same sparkling mini dress Britney Spears wore for her "Circus" album shoot -- and yes, even her onscreen flame Glen Powell tried to reach her orbit in a full-on NASA suit!

The guest list was astronomical, with Jeff Bezos and wife Lauren Sanchez making a stellar appearance after Sydney -- and Scooter, separately -- attended their June wedding. The Image Direct

Sydney’s IG pics show the galaxy of birthday chaos -- twerking with Sexyy Red , belting k

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