Take a look at the item again:
You might think (A)
that a floor-length dress is conservative
(B) until you see the
one that Christina wears. (C)
A psychedelic swirl of pinks and purples that attracts everyone's
attention.
You wanted to do this:
You might think, that a floor-length dress
is conservative until you see the one that Christina wears. A psychedelic
swirl of pinks and purples that attracts everyone's attention.
Adding a comma after think is an error. That a floor-length dress is conservative is a subordinate clause. When you connect a subordinate clause to the end of a main clause, you generally do not use any punctuation.
You might want to review the rules.
Go back to the sentence to try again.