Property flex-shrink

Specifies how the item will shrink relative to
the rest.

The flex-shrink sets the shrink factor of a
flex item. If the size of all flex items is
larger than the wrapper, items will shrink
according to the flex-shrink factor.

Example

This will allow the item to shrink in width if
there is no space available to fit all flex
items.

.item-2 {
  width: 300px;
  flex-shrink: 1;
}