Make container widget fill parent vertically

The trick is to combine an IntrinsicHeight widget and a Row with crossAxisAlignment: CrossAxisAlignment.stretch

This force the children of Row to expand vertically, but Row will take the least amount of vertical space possible.

Card(
  child: IntrinsicHeight(
    child: Row(
      crossAxisAlignment: CrossAxisAlignment.stretch,
      children: <Widget>[
        Container(
          width: 20.0,
          color: Colors.amber,
        ),
        // Expanded(...)
      ],
    ),
  )
)