#animation {
    width: 300px;
    height: 300px; 
    background-color: yellow;
    animation-name:changeWidth;        ➊
    animation-duration: 3s;            ➋
    animation-iteration-count: 6;      ➌
    animation-timing-function: ease;   ➍
    animation-direction: alternate;    ➎
    animation-delay: 2s;               ➏   
}

/* @keyframes 옆에는 animation-name 속성의 속성값을 입력합니다. */
@keyframes changeWidth{                ➐
   from { width: 300px;}
   to { width: 600px;}
}