.bg {
    width: 100%;
    height: 1000px;
    position: relative;
    background: url(../images/background.png) no-repeat center center;
    background-size: 100% 100%;
}


.content {
    width: 80%;
    margin-left: 10%;
}

.board {
    width: 26%;
    height: 530px;
    margin-left:5%;
    float: left;
    -webkit-transition-property: background-size;
    -webkit-transition-duration: 0.3s;
    -webkit-transition-timing-function: ease;
}

.board1 {
    background: url(../images/1.png) no-repeat center center;
    background-size: 90% auto;
}

.board2 {
    background: url(../images/2.png) no-repeat center center;
    background-size: 90% auto;
}

.board3 {
    background: url(../images/3.png) no-repeat center center;
    background-size: 90% auto;
}

.board:hover{
    background-size: 100% auto;
}