drFabio

function sendMessage () {
      idleButton()
      var feedBack = document.getElementById('feedBack')
      var question = document.getElementById("question").value.trim()
      if (!question || question.length === 0){
        setError('Insira uma pergunta')
        return
      }
      if (question === lastQuestion) {
        setError('Você já perguntou isso....')

drFabio

<p id="feedBack"></p>

drFabio

function enableButton () {
  document.getElementById('sendButton').disabled = false
  document.getElementById('sendButton').innerHTML = 'Enviar'
}
function idleButton () {
  document.getElementById('sendButton').disabled = true
  document.getElementById('sendButton').innerHTML = 'Enviando...'
}

drFabio

var authenticated = false
var userAuthData = null
function handleAuthentication (authData) {
  document.getElementById('accessContainer').style.display= 'none'
  document.getElementById('questionsContainer').style.display= 'block'
  authenticated = true
  userAuthData = authData
  document.getElementById('userName').innerHTML = authData.user.displayName
}

drFabio

<div id="questionsContainer">
  <label for="question">Qual sua pergunta, <span id="userName"></span>?</label>
  <input id="question" onfocus="clearMessage()" onKeyUp="checkEnter(event)"></input>
  <p id="feedBack"></p>
  <button id="sendButton" onClick="sendMessage()">Enviar</button>
</div>

drFabio

  <div id="questionsContainer">
    <label for="question">Qual sua pergunta, <span id="userName"></span>?</label>
    <input id="question"></input>
    <p id="feedBack"></p>
    <button id="sendButton" onClick="sendMessage()">Enviar</button>
  </div>

drFabio

var config = {
  apiKey: "ALGUMA_CHAVE",
  authDomain: "pergunteaodev.firebaseapp.com",
  databaseURL: "https://pergunteaodev.firebaseio.com",
  projectId: "pergunteaodev",
  storageBucket: "",
  messagingSenderId: "974289796926"
}
firebase.initializeApp(config)
var databaseRef = firebase.database().ref().child('questions')

drFabio

footer {
  position: fixed;
  bottom: 0;
  width: 100%;
}

drFabio

#logo {
  height: 10vh;
  margin-bottom: 2rem;
}
label {
  font-size: 1.5em;
}

drFabio

<link href="https://fonts.googleapis.com/css?family=Oswald" rel="stylesheet">
<link href="https://maxcdn.bootstrapcdn.com/font-awesome/4.7.0/css/font-awesome.min.css" rel="stylesheet">