Flexbox: how to combine variable and fixed widths

Question

I am trying to achieve a grid with three columns:

• The first column is 50% in width
• The second and third column combined are also 50% in width
• The third columns width is variable; it should grow however it seems fit (it contains one button with variable text).

If column three ends up taking x% of width than column two should be 50-x% in width.

Answer 1

Give the first item flex-basis: 50% and the middle flex-grow: 1.

This will make the first 50% wide, the last as wide as its content and the middle fill the remaining space left

.wrapper {
  display: flex;
}

.wrapper .item {
  border: 1px dotted gray;
}

.wrapper .item:first-child {
  flex-basis: 50%;
}

.wrapper .item:nth-child(2) {
  flex-grow: 1;
}

<div class="wrapper">
  <div class="item">50%
  </div>
  <div class="item">Fill remaining
  </div>
  <div class="item">Button
  </div>
</div>