index.css

body {
    background-color:cornsilk;
    z-index: 10;
    position: relative;
    text-align: center;
}
.button{
    color: rgb(39, 39, 39);
    background-color: cornsilk;
    border-style: solid;
    border-color: rgb(39, 39, 39);
    border-width: 5px;
    width: 200px;
    height: 100px;
    min-height: 30px;
    font-size: 28px;
    transition-duration: 0.3s;
    position: relative;
    margin-top: 20px;
}
.button:hover,.in:hover{
    background-color: rgb(39, 39, 39);
    color: cornsilk;
}
#cover{
    position: initial;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    background-color: rgba(39, 39, 39, 0);
    z-index: 1;
    transition-duration: 0.5s;
}
#toloadin,#author{
    height: 40%;
    width:60%;
    position: fixed;
    left: 20%;
    top: -100%;
    border-radius: 5%;
    padding: 10px;
    background-color: rgb(248, 255, 153);
    z-index: 200;
    box-shadow: rgb(39, 39, 39) 5px 5px 5px;
    transition-duration: 0.5s;
    text-align: center;
}
#tanchuin{
    height: 40%;
    width: 80%;
}
.in{
    width: 150px; 
    height: 80px;
    background-color:rgb(248, 255, 153)
}