style.css

body {
    background-image: linear-gradient( darkslategray, lightgray);
    height: 100%;
}

nav {
    padding-bottom: 80px;
}

nav h1 {
    position: absolute;
    text-align: center;
    color: #fff;
    font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, Oxygen, Ubuntu, Cantarell, 'Open Sans', 'Helvetica Neue', sans-serif;
    font-weight: 800;
    font-size: 23px;
    padding-left: 25%;
}

.image img {
    width: 60px;
    height: 60px;
    border-radius: 30px;
    display: block;
    margin: auto;
}

.container {
    max-width: 1000px;
    margin: auto;
    height: 80vh;
    font-size: 18px;
    font-weight: 900;
    border: 1px solid white;
    border-radius: 10px;
    overflow-y: auto;
    margin-bottom: 30px;
}

.message {
    background-color: white;
    margin: 20px 10px;
    border: 1px solid black;
    border-radius: 5px;
    padding-left: 20px;
    padding-right: 20px;
}

.left {
    float: left;
    clear: both;
}

.right {
    float: right;
    clear: both;
}

#sendcontainer {
    display: block;
    margin: auto;
    max-width: 1140px;
    text-align: center;
}

#messageinp {
    width: 80%;
    border: 1px solid black;
    border-radius: 8px;
    height: 30px;
}

.btn {
    cursor: pointer;
    height: 34px;
    border-radius: 5px;
    width: 80px;
}