Set div to have its siblings width

Answer 1

Here's another Flexbox solution which allows for the second child to wrap to match the width of the variable height sibling.

.wrapper > div {
  border: 1px solid;
}

.child {
  display: flex;
}

.child div {
  flex-grow: 1;
  width: 0;
}

.wrapper {
  display: inline-block;
}

    
This div is dynamically sized based on its content
    
This div will always be the same width as the preceding div, even if its content is longer (or shorter too).

Edit:

To support multiple divs under .child, where each div is on its own line, add break-after: always; ...

.child div {
  flex-grow: 1;
  width: 0;
  break-after: always;
}