style.css

* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
}
.chatbox {
    margin-top: 10px;
    margin-bottom: 10px;
}
.send {
    height: 70px;
}
.responsive-img-cus {
    height: auto;
    max-width: 80%;
    margin-left: auto;
    margin-right: auto;
    display: block;
}
.send-mess {
    height: 70px;
    width: 100%;
    position: fixed;
    bottom: 0;
}
.mess-content {
    padding: 10px;
    display: inline-block;
    border-radius: 10px;
}
.file-field1 {
    position: relative;
}
.file-field1 input[type="file"] {
    position: absolute;
    top: 0;
    right: 0;
    left: 0;
    bottom: 0;
    width: 100%;
    margin: 0;
    padding: 0;
    padding-top: 0px;
    padding-right: 0px;
    padding-bottom: 0px;
    padding-left: 0px;
    font-size: 20px;
    cursor: pointer;
    opacity: 0;
}
button#send-btn {
    margin-top: 15px;
}
@media only screen and (min-width: 993px) {
    nav a.sidenav-trigger {
        display: none !important;
    }
}