Compressing flex boxes when there is not enough space in CSS

Let's say we have three flex boxes, arranged in a row inside a parent. Each child box is set to a width of 100px, and their parent is set to 300px:

Let's add more blocks so that the total width of these child blocks is greater than the width of their parent. In this case, you will see an unexpected effect - the width of the blocks will decrease so that they all fit into their parent, despite the fact that the child blocks are explicitly given a width: