In Flexitive, you can set an element in a design to either have their aspect ratio Locked or Unlocked.
When the aspect ratio of an element is Locked, the aspect ratio of the element remains the same as you resize the bounding box. With aspect ratio Locked, you can use the Fit and Fill settings in the Size and Position panel to crop your element. Unlocking the aspect ratio of an element with a Locked aspect ratio will stretch the element to all edges of the bounding box.
In Flexitive, the Aspect Ratio settings for elements are located in the Size and Position panel.