The Style section
The "Style" section in Mail Designer 365 allows you to format text or objects within an image area from one central place. Depending on the element you have selected, you will see the corresponding style options in the sidebar.
Text Area: Style, Body Text, Emphasis, List, Link
Shape: Link & Background, Fill, Position, Size, Rotate, Flip, Align, Group, Border, Shadow
Image Area: Comment, Link, Alt Text, Optimize, Edit Background, Delete & Zoom, Library
Search through the manual