CSS Property:
flex-wrap:

Note: Internet Explorer 10 and earlier versions do not support the flex-wrap property.

Result:
A
B
C
D
E
F
CSS Code:
#main {
  width:150px;
  height:150px;
  border:1px solid black;
  display:flex;
  flex-wrap: nowrap;
}
Click the property values above to see the result
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