https://codepen.io/joe_bacal/pen/gxMaqz

<!-- html -->
<p>What color is the sky?</p>
<input id="theirAnswer">
<button id="answerButton">Answer</button>

<div class="result right">You got it right!</div>
<div class="result wrong">Sorry, you got it wrong.</div>

/* css */
.result {
  display:none;
}

//js
var btn = document.querySelector('#answerButton');
var right = document.querySelector('.right');
var wrong = document.querySelector('.wrong');

btn.addEventListener('click', function(){
  checkAnswer();
});

function checkAnswer(){
  var ans = document.querySelector('#theirAnswer').value;

  if ( ans == 'blue' || ans == 'Blue '){
    wrong.style.display = 'none';
    right.style.display = 'inline';
  } 

  else {
    right.style.display = 'none';
    wrong.style.display = 'inline';
  }
}