style.css

*{
    margin: 0;
    padding: 0;
    overflow: hidden;
    box-sizing: border-box;
}
body{
    background-color: darkgreen;
    display: flex;
    justify-content: center;
    align-items: center;
    height: 100vh;
    font-family: sans-serif;
}

div#field{
    border: 2px solid gainsboro;
    width: 800px;
    height: 400px;
    position: relative;
}
div#field::after,
div#field::before
{
    border: 2px solid gainsboro;
    width: 80px;
    height: 200px;
    content: '';
    position: absolute;
    top: 100px;
    left: -2px;
}
div#field::after{
    left: auto;
    right: -2px;
}
.lobby{
    width: 400px;
    height: 300px;
    background-color: grey;
    position: fixed;
    box-shadow: 2px 2px 2px black;
    border-radius: 3px;
    display: flex;
    flex-direction: column;
    padding: 1em;
    justify-content: space-around;
}
.lobby h1{
    text-align: center;
    color: seashell;
    
}
.lobby ul{
    background: white;
    padding:  .5em;
    border-radius: .2em;
}
.lobby ul li{
    background: gainsboro;
    list-style: none;
    border-radius: 3px;
    padding: .2em;
    box-shadow: 1px 1px 2px black;
    user-select: none;
    margin: .5em;
}
.lobby ul li:hover{
    background-color: gray;
    color: white;
    cursor: pointer;
}
.lobby input{
    width: 100%;
    padding: 1em;
}