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HTML 

              
                <h1><a href="https://material.io/design/components/text-fields.html">Material Design</a> like form input text fields</h1>

<div class="container">
  <form novalidate>
    <div class="row">
      <div class="col-sm">
        <div class="form-field">
          <div class="form-field__control">
            <label for="firstname" class="form-field__label">First name</label>
            <input id="firstname" type="text" class="form-field__input" />
          </div>
        </div>
      </div>
      <div class="col-sm">
        <div class="form-field">
          <div class="form-field__control">
            <label for="lastname"class="form-field__label">Last name</label>
            <input id="lastname" type="text" class="form-field__input" />
          </div>
        </div>
      </div>
    </div>
    <div class="row">
      <div class="col-sm">
        <div class="form-field">
          <div class="form-field__control">
            <label for="email" class="form-field__label">Email</label>
            <input id="email" type="email" class="form-field__input" />
          </div>
        </div>
      </div>
    </div>
    <div class="row">
      <div class="col-sm">
        <div class="form-field">
          <div class="form-field__control">
            <label for="street"class="form-field__label">Street address</label>
            <input id="street" type="text" class="form-field__input" />
          </div>
        </div>
      </div>
    </div>
    <div class="row">
      <div class="col-sm">
        <div class="form-field">
          <div class="form-field__control">
            <label for="zip"class="form-field__label">Zip code</label>
            <input id="zip" type="text" class="form-field__input" />
          </div>
        </div>
      </div>
      <div class="col-sm">
        <div class="form-field">
          <div class="form-field__control">
            <label for="city"class="form-field__label">City</label>
            <input id="city" type="text" class="form-field__input" />
          </div>
        </div>
      </div>
    </div>
    <div class="row">
      <div class="col-sm">
        <div class="form-field">
          <div class="form-field__control">
            <label for="additionalInfo" class="form-field__label">Additional info</label>
            <textarea id="additionalInfo" class="form-field__textarea"></textarea>
          </div>
        </div>      
      </div>
    </div>
  </form>
</div>

<p style="text-align:center">Read more: <a href="https://auralinna.blog/post/2018/how-to-create-material-design-like-form-text-fields" target="_blank" rel="noopener noreferrer">How to create Material Design like form text fields with floating label and animated underline bar</a></p>

<p style="text-align:center">See also: <a href="https://codepen.io/teroauralinna/pen/JeKrXe" target="_blank">CSS only version</a></p>
!

CSS 

              
                html, body {
  color: #333;
  font-size: 16px;
  line-height: 20px;
}
body {
  margin: 20px;
}

h1 {
  line-height: 1.2;
  margin-bottom: 35px;
  text-align: center;
}

.container {
  margin: 0 auto 35px;
  max-width: 450px;
}

/* Actual code example */

$primary-color: #b11adc;
$animation-duration: 0.4s;

@mixin label-active() {
  font-size: 0.75rem;
  transform: translateY(-14px);
}

.form-field {
  display: block;
  margin-bottom: 16px;
  
  &--is-active {
    .form-field__control {
      &::after {
        border-bottom: 2px solid $primary-color;
        transform: scaleX(150);
      }
    }
    .form-field__label {
      color: $primary-color;
      @include label-active();
    }
  }
  &--is-filled {
    .form-field__label {
      @include label-active();
    }
  }
}
.form-field__label {
  display: block;
  font-size: 1.2rem;
  font-weight: normal;
  left: 0;
  margin: 0;
  padding: 18px 12px 0 ;
  position: absolute;
  top: 0;
  transition: all $animation-duration;
  width: 100%;
}
.form-field__control {
  background: #eee;
  border-radius: 8px 8px 0 0;
  overflow: hidden;
  position: relative;
  width: 100%;
  
  &::after {
    border-bottom: 2px solid $primary-color;
    bottom: 0;
    content: "";
    display: block;
    left: 0;
    margin: 0 auto;
    position: absolute;
    right: 0;
    transform: scaleX(0);
    transition: all $animation-duration;
    width: 1%;
  }
}
.form-field__input,
.form-field__textarea {
  appearance: none;
  background: transparent;
  border: 0;
  border-bottom: 1px solid #999;
  color: #333;
  display: block;
  font-size: 1.2rem;
  margin-top: 24px;
  outline: 0;
  padding: 0 12px 10px 12px;
  width: 100%;
}
.form-field__textarea {
  height: 150px;
}
!

JS 

              
                const setActive = (el, active) => {
  const formField = el.parentNode.parentNode
  if (active) {
    formField.classList.add('form-field--is-active')
  } else {
    formField.classList.remove('form-field--is-active')
    el.value === '' ? 
      formField.classList.remove('form-field--is-filled') : 
      formField.classList.add('form-field--is-filled')
  }
}

[].forEach.call(
  document.querySelectorAll('.form-field__input, .form-field__textarea'),
  (el) => {
    el.onblur = () => {
      setActive(el, false)
    }
    el.onfocus = () => {
      setActive(el, true)
    }
  }
)
!
999px

Console