If Ofelia's green silk dress getup looked familiar, you may have been reminded of the outfit Alice wore in Disney's 1951 adaptation of the Lewis Carroll novel Alice's Adventures in Wonderland.
Just like Alice, who crawls down a rabbit hole into a very strange world of fantasy, Ofelia also crawls through the hole in the fig tree and into her fantasy world.
The dress is, which is also depicted on the drawings of Ofelia in the Book of Crossroads, is more of an one off allusion than of any real symbolic significance. But just because Alice's and Ofelia's adventures are very different, they're still both stories of a young female protagonist looking for some respite from the human world.
And, although Alice's story might have a bit more levity, they both run into some disturbing things when they enter their respective wonderlands.