このドレスは君にぴったり合っている。

this (something or someone close to the speaker (including the speaker), or ideas expressed by the speaker)

dress

topic marker particle; indicates contrast with another option (stated or unstated); adds emphasis

you; buddy; pal; monarch; ruler; sovereign; (one's) master

at (place, time); in; on; during; to (direction, state); toward; into; for (purpose); because of (reason); for; with; by; from; as (i.e. in the role of); per; in; for; a (e.g. "once a month"); and; in addition to; if; although

tightly; closely; exactly; precisely; suddenly (stopping); perfectly (suited); ideally

to come together; to merge; to unite; to meet; to fit; to match; to suit; to agree with; to be correct; to be profitable; to be equitable; to do ... to each other; to do ... together