Update
If you need to keep inline-block
styles, you need the .left
and .right
div
s to add up to 800px
. The thing with inline-block
is that it will include white space and add it to the width. This is why the wrapping is still occurring. The following image shows the white space that is causing the wrapping.

There are many ways to remove white space and make this fit. One way is to add an HTML
comment between the .left
and right
div
, which removes all white space.
<div class="container">
<div class="left"></div><!--
--><div class="right">
<div class="red-yellow">
<div class="red"></div>
<div class="yellow"></div>
</div>
</div>
</div>
Demo
* {
margin: 0;
padding: 0;
box-sizing: border-box;
}
.container {
margin: 0 auto;
width: 800px;
}
.left, .right, .red, .yellow {
display: inline-block;
vertical-align: top;
}
.left {
width: 250px;
height: 500px;
background: gray
}
.right {
width: 550px;
height: 550px;
background: blue;
}
.red {
background: red;
width: 275px;
height: 200px;
}
.yellow {
background: yellow;
width: 275px;
height: 200px;
}
<div class="container">
<div class="left"></div><!--
--><div class="right">
<div class="red-yellow">
<div class="red"></div>
<div class="yellow"></div>
</div>
</div>
</div>
If you add display: flex
to the .container
, the immediate children (.left
and .right
) will align in the same row. The .right
div
is 50px
taller than the .left
div
because of the explicit width being set (550px
for .right
, 500px
for .left
).
Also, you can remove this, as it will no longer have any effect due to the flexbox
container.
.left, .right, .red, .yellow {
display: inline-block;
vertical-align: top;
}
Demo
* {
margin: 0;
padding: 0;
box-sizing: border-box;
}
.container {
margin: 0 auto;
width: 800px;
display: flex;
}
.left {
width: 250px;
height: 500px;
background: gray
}
.right {
width: 550px;
height: 550px;
background: blue;
}
.red {
background: red;
width: 275px;
height: 200px;
}
.yellow {
background: yellow;
width: 275px;
height: 200px;
}
<div class="container">
<div class="left"></div>
<div class="right">
<div class="red-yellow">
<div class="red"></div>
<div class="yellow"></div>
</div>
</div>
</div>