document.body.style.background = '#313131';
var messages = document.getElementsByClassName("messages");

for (var i = 0; i < messages.length; i++) {
    messages[i].style.background = '#515151';
    messages[i].style.borderColor = '#212121';
}

var username = document.getElementsByClassName("username");
for (var i = 0; i < username.length; i++) {
    username[i].style.color = '#fff';
}

var content = document.getElementsByClassName("content");
for (var i = 0; i < content.length; i++) {
    content[i].style.color = '#fff';