div.main {
    background: url(/images/4.jpg);
    background-size: cover;
    width: 100%;
    min-height: 100vh;
    max-height: 100%;
    position: absolute;
    top: 0;
    left: 0;
    margin: 0 auto;
}
.down {
    font-size:22px;
    font-weight:bold;
    color: #fff;
    text-align: center;
    position: absolute;    
    top: -webkit-calc(70% - 166px);
    top: -moz-calc(70% - 166px);
    top: calc(70% - 166px);
    left: -webkit-calc(50% - 248px);
    left: -moz-calc(50% - 248px);
    left: calc(50% - 315px)
}

.butn {
    background: #9e9e9e;
    background-image: -webkit-linear-gradient(top, #9e9e9e, #000000);
    background-image: -moz-linear-gradient(top, #9e9e9e, #000000);
    background-image: -ms-linear-gradient(top, #9e9e9e, #000000);
    background-image: -o-linear-gradient(top, #9e9e9e, #000000);
    background-image: linear-gradient(to bottom, #9e9e9e, #000000);
    -webkit-border-radius: 15;
    -moz-border-radius: 15;
    border-radius: 15px;
    text-shadow: 3px 1px 3px #666666;
    -webkit-box-shadow: 0px 1px 3px #666666;
    -moz-box-shadow: 0px 1px 3px #666666;
    box-shadow: 0px 1px 3px #666666;
    font-family: Arial;
    color: #ffffff;
    font-size: 20px;
    padding: 10px 20px 10px 20px;
    text-decoration: none;
    position: absolute;
    top: 70%;
    left: -webkit-calc(50% - 105px);
    left: -moz-calc(50% - 105px);
    left: calc(50% - 105px);   
    font-size: 30px;
    font-weight: bold;
    width: 210px;
    text-align: center;
    height: 50px;
    line-height: 50px;
}

.butn:hover {
  background: #c2c2c2;
  background-image: -webkit-linear-gradient(top, #c2c2c2, #525252);
  background-image: -moz-linear-gradient(top, #c2c2c2, #525252);
  background-image: -ms-linear-gradient(top, #c2c2c2, #525252);
  background-image: -o-linear-gradient(top, #c2c2c2, #525252);
  background-image: linear-gradient(to bottom, #c2c2c2, #525252);
  text-decoration: none;
}