It's easier if you look. Resize the window's width:
.outer {
background:red;
display: inline-block;
}
.inner-1 {
display:inline-block;
height: 50px;
width:250px;
background:green;
margin-right:50px;
}
.inner-2 {
display:inline-block;
height: 50px;
width:250px;
background:blue;
}
<div class="outer">
<div class="inner-1"></div>
<div class="inner-2"></div>
</div>
Basically, as soon as the blue box wraps the red box should shrink to fit. But the red box continues to behave as though the blue box is on the first line.
I can sort of get there with media queries but even that is a guessing game since I don't know why it's doing this in the first place.