style.css

*{padding: 0;
margin: 0;
box-sizing: border-box;
font-family: 'Noto Sans JP', sans-serif;}

body{display: flex;
justify-content: center;
align-items: center;}

.container{width: 20%;
box-shadow: 0px 0px 5px grey;
position: absolute;
top: 10%;}

.chat-head{display: flex;
background-color: rgb(172, 2, 2);
padding: 10px;
color: wheat;
align-items: center;}

.img{width: 30px;
height: 30px;
border-radius: 50%;
overflow: hidden;
cursor: pointer;}

.img img{width: 100%;
height: 100%;
object-fit: cover;}

.chat-head h4{margin-left: 10px;
cursor: pointer;}

.messages{height: 400px;flex-direction: column;
display: flex;overflow: scroll;}

.messages div{padding: 5px;min-width: 20%;max-width: 80%;
background-color: lightgrey;border-radius: 5px;margin: 3px;
margin-bottom: 7px;color: black;
font-size: 14px;word-wrap: break-word;margin-left: 7px;}

.messages div:focus{background-color:rgb(172, 2, 2); color: wheat;}

.type a{float: right;margin-right: 5px;
text-decoration: none;
color:rgb(172, 2, 2);
font-size: 16px;}

.type{width: 100%;
padding: 5px;
background-color: lightgrey;}

.type input{border-radius: 5px;
border: none;
outline: none;font-size: 14px;width: 88%;
padding: 3px;}

.sign-box{
    background-color:rgb(233, 231, 231);
    width: 30%;
    text-align: center;
    z-index: 3;
    height: 350px;
    margin-top: 120px;
    padding: 20px;
    border-radius: 20px;
    opacity: 0;
    pointer-events: none;
    transition: 0.8s;
}

.sign-box input{
    width: 80%;
    margin: 5px;
    padding: 5px;
    border: none;
    outline: none;
}

.sign-box h2{
    color: rgb(172, 2, 2);
    margin: 10px;
}

.sign-box button{
    margin: 5px 15px;
    background-color: rgb(172, 2, 2);
    color: white;
    padding: 8px;
    font-size: 16px;
    cursor: pointer;
    border: none;
    border-radius: 20px;
transition: 0.5s;
outline: none;
}

.sign-box button:hover{ background-color: rgb(226, 226, 226);
color: rgb(172, 2, 2);
border: 1px solid rgb(172, 2, 2);}

/* @media screen and (max-width:1000px){
    .container{width: 50%;}
    .sign-box{width: 55%;}
} */

@media screen and (max-width:1000px){
    .messages{height: 86vh;}
    .container{width: 100%;height: 100vh;top: 0%;}
    .sign-box{width: 90%;height: 300px;margin-top: 100px;}
}