Line an 8×8-inch baking dish with parchment paper.
In a saucepan, melt dark chocolate chips, condensed milk, and butter until smooth.
Stir in vanilla extract and pour mixture into pan, smoothing surface.
Melt white chocolate, divide, and tint one red and one gray or black.
Drizzle colored chocolates over the base and swirl gently for a marbled effect.
Lightly dust with silver glitter for a shimmering look.
Refrigerate 2 hours or until firm, then slice and serve.
