Enjoy Your Special Day! Happy Birthday Card for Sister: Shiny, party balloons can't be beat! This hot pink birthday card for your sister is a fantastic way to say "Happy Birthday!" to a sister who really shines. Flower power balloons, heart balloons, and striped balloons, this birthday card is for a sister who loves a celebration. It's easy to wish your sister a great birthday-just send a special birthday card and she's sure to smile!