Nice Animated Input Labels with Pure CSS

A pure CSS / CSS3 approach to building nice floating form labels using sibling selectors and pseudo classes. Based on a UI concept by Matt D. Smith.

How to use it:

Create labels for input fields.

<form>
  <input type="text" name="name" class="question" id="nme">
  <label for="nme"><span>What's your name?</span></label>
  <textarea name="message" class="question" id="msg"></textarea>
  <label for="msg"><span>What's your message?</span></label>
</form>

Basic CSS styles.

input, label, textarea {
  display: block;
  margin: 10px;
  padding: 5px;
  border: none;
  font-size: 22px;
}
textarea:focus, input:focus { outline: 0; }
input.question, textarea.question {
  font-size: 48px;
  font-weight: 300;
  border-radius: 2px;
  margin: 0;
  border: none;
  width: 80%;
  background: rgba(0, 0, 0, 0);
  transition: padding-top 0.2s ease, margin-top 0.2s ease;
  overflow-x: hidden; /* Hack to make "rows" attribute apply in Firefox. */
}

The Core CSS styles for the underline and floating labels.

input.question + label, textarea.question + label {
  display: block;
  position: relative;
  white-space: nowrap;
  padding: 0;
  margin: 0;
  width: 10%;
  border-top: 1px solid red;
  -webkit-transition: width 0.4s ease;
  transition: width 0.4s ease;
  height: 0px;
}
input.question:focus + label, textarea.question:focus + label { width: 80%; }
 input.question:focus, input.question:valid {
 padding-top: 35px;
}
textarea.question:valid, textarea.question:focus {
 margin-top: 35px;
}
input.question:focus + label > span, input.question:valid + label > span {
 top: -100px;
 font-size: 22px;
 color: #333;
}
textarea.question:focus + label > span, textarea.question:valid + label > span {
 top: -150px;
 font-size: 22px;
 color: #333;
}
input.question:valid + label, textarea.question:valid + label {
 border-color: green;
}
input.question:invalid, textarea.question:invalid {
 box-shadow: none;
}
input.question + label > span, textarea.question + label > span {
  font-weight: 300;
  margin: 0;
  position: absolute;
  color: #8F8F8F;
  font-size: 48px;
  top: -66px;
  left: 0px;
  z-index: -1;
  -webkit-transition: top 0.2s ease, font-size 0.2s ease, color 0.2s ease;
  transition: top 0.2s ease, font-size 0.2s ease, color 0.2s ease;
}
input[type="submit"] {
  -webkit-transition: opacity 0.2s ease, background 0.2s ease;
  transition: opacity 0.2s ease, background 0.2s ease;
  display: block;
  opacity: 0;
  margin: 10px 0 0 0;
  padding: 10px;
  cursor: pointer;
}
input[type="submit"]:hover { background: #EEE; }
input[type="submit"]:active { background: #999; }
input.question:valid ~ input[type="submit"], textarea.question:valid ~ input[type="submit"] {
 -webkit-animation: appear 1s forwards;
 animation: appear 1s forwards;
}
input.question:invalid ~ input[type="submit"], textarea.question:invalid ~ input[type="submit"] {
 display: none;
}