How to make text input box to occupy all the remaining width within parent block?

Question

How do achieve the following:

┌────────────────────parent────────────────────┐
│ label [text-box                   ] [button] │
│ paragraph                           


        

Answer 1

I don't like first answer with the "table-less" version that actually uses table-cell. Nor the second answer that uses actual tables. Nor third answer that uses hardcoded widths. Here is solution using flex. It is by far simplest:

#parent {
  display: flex;
}
input {
  flex: 1;
}

  Name
  
  Button

paragraph