*{
    margin: 0;
    padding: 0;
}
a{
    text-decoration: none;
}
kbd{
    border: 1px solid red;
    width: 4em;
    height: 4em;
    display: inline-block;
    text-transform: uppercase;
    position: relative;
}
kbd>button{
    position: absolute;
    bottom: 0;
    right: 0;
    display: none;
    font-size: 12px;
    background: #000;
    color: white;
    border: none;
}
kbd:hover>button{
    display: inline-block;
}
body{
    background:grey url(./wall.jpg) no-repeat center center;
    background-size: cover;
}
main{
    text-align: center;
    display: flex; /*使main变成弹性盒子*/
    justify-content: center;  /*水平居中*/
    align-items: center; /*垂直居中*/
    height: 100vh;  /*vh--viewport height 视口高度*/

}
#main{
    display: inline-block;
    background: rgba(255,255,255,0.2);
    border-radius: 10px;
    padding: 0 10px;
}
#main>div:nth-child(2){
    margin-left: -20px;
}
#main>div:nth-child(3){
    margin-left: -78px;
    margin-bottom: 16px;
}
.key{
    width: 50px;
    height: 40px;
    background: -webkit-linear-gradient(top, #292929 0%,#111111 100%);
    color: #c5c5c5;
    border: none;
    border: 1px solid #373737;
    border-radius: 5px;
    box-shadow: 0 0 0 1px #1a1b1c,0 0 0 2px #1F2020,0 3PX 0 2px #080808;
    /* display: inline-flex;
    align-items: center;
    justify-content: center; */
    margin: 0 6px;
    font-size: 16px;
    font-family: Helvetica;
    position: relative;
}
.row{
   margin-top: 16px;
}
.key img{
    width: 16px;
    height: 16px;
    position: absolute;
    left: 4px;
    bottom: 2px;
}
.key .text{
    position: absolute;
    top: 2px;
    left: 4px;
}