.box {width: 680px;
margin: 40px auto; display:flex; flex-wrap: wrap; }

.season-box {width:330px;
height: 214px;
border-radius: 5px;
display: block;
margin:5px;
background-size: 100%;
background-repeat: no-repeat;
opacity: 0.5;
transition: opacity 2s;}

.season-box:hover {opacity: 1.0;}

.winter {background-image: url("images/winter.jpg");}

.spring {background-image: url("images/spring.jpg");}

.summer {background-image: url("images/summer.jpg");}

.fall {background-image: url("images/fall.jpg");}