html and css

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>animated email input box</title>
    <style>
    body {
   background-color: #485461;
background-image: linear-gradient(315deg, #485461 0%, #28313b 74%);
        height: 100vh;
  font-family: 'Roboto Mono', monospace;
}

*:focus {outline: none;}

.wrap {
  height: 100%;
  width: 100%;
  overflow: hidden;
  padding: 15px;
}
.form-wrap {
    position: relative;
    height: 50px;
    width: 400px;
    margin: 100px auto 0;

}

input {
  color: #fff;
  position: absolute;
  width: 100%;
  height: 100%;
  left: 0;
  padding-top: 5px;
  border: none;
  font-size: 1.5em;
  font-weight: 200;
  background: none;
  opacity: 0;
    font-family: 'Roboto Mono', monospace;
  transition: all 0.5s ease;
}

.active input{
  opacity: 1;
  transition: all 0.5s ease 0.5s;
}

svg {
  position: absolute;
  left: 0;
  top: 100%;
  overflow: visible;
  fill: none;
  z-index: 5;
}

label {
  color: #fff;
  position: absolute;
  top: 15px;
  font-size: 1.3em;
  transition: all 0.5s ease;
}

.active label {
  top: 0px;
  font-size: 1.6em;
  color: #FF5252;
  transition: all 0.5s ease 0.6s;
}

svg path {
  stroke: #fff;
  stroke-width: 3px;
}

.active + svg path {
  stroke: #FF5252;
  transition: stroke 0.4s ease 0.6s;
}

.input {
  height: 100%;
  width: 100%;
  position: relative;
  overflow: hidden;
}
.input:before {
    content: "";
    position: absolute;
    height: 26px;
    width: 3px;
    right: 15px;
    bottom: -50px;
      background-color: transparent;
   transform-origin: inherit;
    transform: rotate(0deg);
    transition: transform 0.4s ease , bottom 0.4s ease 0.3s, background-color 0.2s ease 0.6s ;
}

.input:after {
    content: "";
    position: absolute;
    height: 26px;
    width: 3px;
    right: 15px;
    bottom: -50px;
    visibility: hidden;
     background-color: transparent;
     transform-origin: inherit;
    transform: rotate(0deg);
    transition: transform 0.4s ease, visibility 0.4s ease, bottom 0.4s ease 0.3s, background-color 0.2s ease 0.6s, height 0.2s ease 0.6s;
}

.valid:before {
  bottom: 10px;
   right: 16px;
  visibility: visible;
   background-color: #4CAF50 ;
     transform-origin: inherit;
  transform: rotate(40deg);
  transition: bottom 0.4s ease, transform 0.4s ease 0.3s;
  }

.valid:after {
  bottom: 10px;
   height: 15px;
  visibility: visible;
  background-color: #4CAF50;
    transform-origin: inherit;
  transform: rotate(-45deg);
  transition: bottom 0.4s ease, visibility 0.4s ease 0.3s, transform 0.4s ease 0.3s;
  }

  .invalid:before {
    bottom: 10px;
    visibility: visible;
    background-color: #ff5252;
    transform: rotate(40deg);
    transition: bottom 0.4s ease, transform 0.4s ease 0.3s;
    }

  .invalid:after {
    height: 26px;
    bottom: 10px;
    visibility: visible;
    background-color: #ff5252;
    transform: rotate(-45deg);
    transition: bottom 0.4s ease, visibility 0.4s ease 0.3s, transform 0.4s ease 0.3s;
    }
    </style>
</head>
<body>
   <br><br><br><br><br><br><br><br><br>
    <div class="form-wrap">
  <div class="input">
<label for="mail">Email address</label>
<input type="email" name="mail" autocomplete="off">
</div>
 <svg>
  <path d="M0 1.5h400" fill="none"/>
</svg>
</div>
<script src="snap.svg-min.js"></script>
<script src="scripts.js">
   
    </script>
</body>
</html>

 'use strict';
var textInput = document.querySelector('input');
var textPath;
var textDown = function() {
  textPath.animate({
    d: "M0 1.5c150 40 300 30 400 0"
  }, 150, mina.easeout);
};
var textUp = function() {
  textPath.animate({
    d: "M0 1.5c150-18 300-18 400 0"
  }, 150, mina.easein);
};
var textSame = function() {
  textPath.animate({
    d: "M0 1.5h400"
  }, 200, mina.easein);
};
var textRun = function() {
  setTimeout(textDown, 200);
  setTimeout(textUp, 400);
  setTimeout(textSame, 600);
};
(function() {
  textInput.addEventListener('focus', function() {
    var svgText = Snap('svg');
    var parentDiv = this.parentElement;
    textPath = svgText.select('path');
    parentDiv.classList.add('active');
    textRun();
    this.addEventListener('blur', function() {
      var rg = /^([A-Za-z0-9_\-\.])+\@([A-Za-z0-9_\-\.]{3,9})+\.([A-Za-z]{2,4})$/;
      this.value == 0 ? parentDiv.classList.remove('active') : null;
      !rg.test(this.value) && this.value != 0 ?
        (parentDiv.classList.remove('valid'), parentDiv.classList.add('invalid'), parentDiv.style.transformOrigin = "center") :
        rg.test(this.value) && this.value != 0 ?
        (parentDiv.classList.add('valid'), parentDiv.classList.remove('invalid'), parentDiv.style.transformOrigin = "bottom") : null;
    });
    parentDiv.classList.remove('valid', 'invalid')
  });
})();

在线演示

让链接同时具备两种打开方式