width: 320px;
    height: 240px;
    font: 900 24px Roboto;
    display: flex;
    align-items: center;
    justify-content: center;
}
.red-box {
    background-color: #ef5350; /* red 400 */
    padding: 16px;
    color: #ffffff;

width: 100%;
    max-width: 240px;
}

width: 320,
  
  height: 240,
  color: Colors.grey[300],
  child: Center(
    child: Container(
      // red box