The flex property is a shorthand property for:
The flex property sets the flexible length on flexible items.
Note: If the element is not a flexible item, the flex property has no effect.
Note: Internet Explorer 9 and earlier versions do not support the flex property.
Note: Internet Explorer 10 supports an alternative, the -ms-flex property. IE11 and newer versions fully support the flex property (do not need the -ms- prefix).