blue pageant dress Champagne/Sky Spaghetti Strap Appliqued Lace Mermaid Prom Dresses ARD2857 Featuring a sweetheart neckline Sherri Hill Pageant Pageant Dresses

FIT: Runs slightly small

Exceptions are extremely rare Black-tie optional events Homecoming-style teen black-tie Daytime semi-formal receptions If the dress ends above the knee, it is almost always too casual

A selfie taken with the help of a mirror showed the mom of two in a relaxed mode as family photos decorated the staircase wall behind her

Playing all of Abba's hits is a must, especially "Dancing Queen." Disco ball decorations, '70s attire and portable karaoke microphones party favors will make for the perfect Mamma Mia!-themed celebration

USA TODAY Network asked experts to explain what's going on with the dress that mesmerized the Internet