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HTML

CSS

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HTML

              
                <form>
  <input id="example-input-1" type="text" name="Name">
  <div class="flex-container">
    <div class="flex-spacer"></div>
    <label for="example-input-1">Type Something!</label>
  </div>
</form>
              
            
!

CSS

              
                body * {
  box-sizing: border-box;
  font-family: sans-serif;
  font-size: 16px;
}

form {
  position: relative;
  width: 100%;
}

input,
.flex-container {
  line-height: 20px;
  border-radius: 3px;
  transition: all .4s ease-out;
}

input {
/*set z-index of input higher than that of label so hover states and clicks get registered on input element*/
  z-index: 1;
  position: relative;
  width: 100%;
  padding: 20px;
/*transparent background allows label text to be seen, even though input is on top of label*/
  background-color: transparent;
  border: 2px solid black;
}

input:focus {
  outline: none;
}

.flex-container {
  display: flex;
  flex-flow: row nowrap;
  position: absolute;
  top: 0;
  left: 0;
  width: 100%;
}

.flex-spacer,
label {
  flex-grow: 0;
  position: relative;
  border-radius: inherit;
  transition: inherit;
}

.flex-spacer {
  background-color: #DDD;
}

label {
  color: #777;
/*padding of input + border of input*/
  padding: 22px;
}

/*class="not-empty" added to input elements when text is added to the input field*/
input.not-empty {
    border-color: #F75;
}

input.not-empty + .flex-container .flex-spacer {
  flex-grow: 1;
}

input.not-empty + .flex-container label {
/*set z-index of label higher than that of input so text gets hidden behind label*/
  z-index: 2;
  color: #FFF;
  background-color: #F75;
}
              
            
!

JS

              
                function handleInput() {
  if (this.value != "") {
    this.classList.add("not-empty");
  } else {
    this.classList.remove("not-empty");
  }
}

var field = document.querySelector("input");

field.addEventListener("input", handleInput);
              
            
!
999px

Console