https://www.cnet.com/news/microsoft-office-app-icons-get-a-new-simplified-look/

The new icons show two separate panels: one with a letter on it (such as a W for Word), and another with an app symbol (such as lines of text for Word). The previous icon design merged the two panels. 

"This allows us to maintain familiarity while still emphasizing simplicity when inside the app," Microsoft said in its blog post.