In this case, flexbox actually is a bit awkward - one is often forced to pair flexbox with calc in this sort of situation. If the content, including text, is to

In this case, flexbox actually is a bit awkward - one is often forced to pair flexbox with calc in this sort of situation. If the content, including text, is too long, it pushes the right container down a level unless the width is fixed to an appropriate size - this is doable with calc (for fluid layout) if one has control over the size of the left container, but otherwise it may be difficult to obtain the desired UI with flexbox.