Colored acrylic coffin nails are popular in summer and Early Fall 2021. What is a coffin nail? Since people began to do nail polish, there are mainly been two shapes: round and square. We can provide different styles of coffin nails. And nail art fans, we finally have something new. Coffin nails, sometimes called ballerina-shaped nails, are a new trend in nail art. They bend almost to the tip, where they are squared to create visual interest and edges.