A flex property with only one value and it being a width value, should be 'flex-basis' according to MDN, however, these two different lines of code give different results.
.box > div {
border: 2px solid rgb(96, 139, 168);
background: rgba(96, 139, 168, .2);
flex: 180px;
.box > div {
border: 2px solid rgb(96, 139, 168);
flex-basis: 180px;