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HTML 

              
                <!DOCTYPE html>
<html lang="en">
<head>
  <script src="//code.jquery.com/jquery-1.11.1.min.js"></script>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1">
  <title>User-Friendley Character Limit UI</title>
</head>
<body>
  
<div class="container">
    <h2>User-Friendly Character Limit UI (WIP)</h2>
    <p>This component is designed to show how to implement a character limit. Start typing and see what happens as you go over the limit.</p>
    
    <div class="characterLimit">
      <label for="message" class="p-b">Your Message:</label>
      <textarea id="message" class="message" name="message" contenteditable="true"></textarea>
      <div class="flex">
        <div>
          <label class="limit">Max 120 Characters</label>
        </div>
        <div>
          <span class="char-left"></span>
          <input type="submit" class="submit" value="Submit" />
        </div>
      </div>
    </div>
    
</div>
  
  
</body>
</html>
!

CSS 

              
                html {
  font-size: 100%;
  -webkit-box-sizing: border-box;
          box-sizing: border-box;
}

*, *::before, *::after {
  -webkit-box-sizing: inherit;
          box-sizing: inherit;
}

body {
  margin: 0px;
  padding: 0px;
  line-height: 1.5;
  font-family: Arial, Helvetica, sans-serif;
  font-size: 18px;
  background-color: #80DEFF;
  color: #353535;
}

.container {
  background-color: white;
  border-radius: 4px;
  max-width: 500px;
  margin: 4rem auto;
  padding: 1.25rem;
  width: 80%;
  -webkit-box-shadow: 1px 3px 10px rgba(0,0,0,.15);  /* Safari 3-4, iOS 4.0.2 - 4.2, Android 2.3+ */
  -moz-box-shadow:    1px 3px 10px rgba(0,0,0,.15); /* Firefox 3.5 - 3.6 */
  box-shadow:         1px 3px 10px rgba(0,0,0,.15);  /* Opera 10.5, IE 9, Firefox 4+, Chrome 6+, iOS 5 */
  
 }

.characterLimit {
  position:relative;
}
.characterLimit label {
  display: block;
}

.characterLimit textarea {
  resize: vertical;
  width: 100%;
  border-radius: 4px;
  border: 1px solid #ccc;
  padding: 1rem 0.5rem;
  min-height: 115px;
  margin-bottom: 0.25rem;
  font-family: Arial, Helvetica, sans-serif;
}
.characterLimit textarea:focus {
  box-shadow: 0 0 2pt 2pt lightblue;
  border-color: lightblue;
  outline: transparent;
  border-radius: 4px;
}

.flex {
  display: flex;
  justify-content: space-between;
  align-items: center;
}
.char-left {
  margin-right: .75rem;
}
.message.warning, .message.warning:focus {
   box-shadow: 0 0 2pt 2pt rgba(255, 0, 0, 0.5);
   border-color: red;
}
.warning {
  color:red;
}
.submit {
  background-color: #3DC08D;
  font-size: 18px;
  color:white;
  border: none;
  border-radius: 4px;
  padding: 0.7rem 1.25rem;
  transition: all 200ms ease-in-out;
}
.submit:hover {
  background-color: #008A5B;
  cursor:pointer;
}

.disable {
  pointer-events: none;
  opacity: 0.5;
}
.p-t {
  padding-top: .75rem;
}
.p-b {
  padding-bottom: .75rem;
}
!

JS 

              
                (function(){
  var msg = document.getElementsByClassName("message")[0],
      charLeftLabel = "char-left",
      charLeft = document.getElementsByClassName(charLeftLabel)[0], 
      textareaLabel = "message",
      maxChar = 120,
      maxCharWarn = 0;
  var submitButton = document.getElementsByClassName("submit")[0],
      submitButtonLabel = "submit";
 
  
  	  // show characters left at start
  	  charLeft.innerHTML = maxChar;

  	  // update while typing
  	  msg.onkeydown = function(){
        setTimeout(function(){
          charLeft.innerHTML = maxChar - msg.value.length;

          // whether or not to display warning class based on characters left
          var warnLabel = msg.value.length >= maxChar ? " warning" : "";
          charLeft.className = charLeftLabel + warnLabel;
          
          var warningLabel = msg.value.length >= maxChar ? " warning" : "";
          msg.className = textareaLabel + warningLabel;
          
          var disableBtn = msg.value.length >= maxChar ? " disable" : "";
          submitButton.className = submitButtonLabel + disableBtn;
          console.log(submitButton);
          
        }, 1); 
      };
})();
!
999px

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