.flash {
  -webkit-animation-name: flash-animation;
  -webkit-animation-duration: 3s;

  animation-name: flash-animation;
  animation-duration: 3s;
}

@-webkit-keyframes flash-animation {  
  from { background: yellow; }
  to   { background: default; }
}

@keyframes flash-animation {  
  from { background: yellow; }
  to   { background: default; }
}