One div dynamic height one div remaining height and scroll

Question

I have 2 divs inside a parent:

Answer 1

You can either use flexbox. no markup changes.

.parent {
  display: flex;
  flex-direction: column;
  height: 100px;
}
.foo2 {
  flex: 1; /*expand to fit*/
  background: silver;
  overflow: auto; /*scroll as needed*/
}

<div class="parent">
  <div class="foo1">1</div>
  <div class="foo2">2<br>2<br>2<br>2<br>2<br>2<br>2<br>2</div>
</div>

Or use CSS table, additional markup is required.

.parent {
  display: table;
  width: 100%;
  height: 100px;
}
.foo1, .foo2 {
  display: table-row;
}
.cell {
  display: table-cell;
  position: relative;
}
.foo2 {
  height: 100%; /*expand to fit*/
  background: silver;
}
.scroll {
  position: absolute;
  top: 0;
  bottom: 0;
  left: 0;
  right: 0;
  overflow: auto; /*scroll as needed*/
}

<div class="parent">
  <div class="foo1">
    <div class="cell">1</div>
  </div>
  <div class="foo2">
    <div class="cell">
      <div class="scroll">2<br>2<br>2<br>2<br>2<br>2<br>2<br>2</div>
    </div>
  </div>
</div>