<!-- Form-->
<div class="form">
  <div class="form-toggle"></div>
  <div class="form-panel one">
    <div class="form-header">
      <h1>Account Login</h1>
    </div>
    <div class="form-content">
      <form>
        <div class="form-group">
          <label for="username">Username</label>
          <input type="text" id="username" name="username" required="required"/>
        </div>
        <div class="form-group">
          <label for="password">Password</label>
          <input type="password" id="password" name="password" required="required"/>
        </div>
        <div class="form-group">
          <label class="form-remember">
            <input type="checkbox"/>Remember Me
          </label><a class="form-recovery" href="#">Forgot Password?</a>
        </div>
        <div class="form-group">
          <button type="submit">Log In</button>
        </div>
      </form>
    </div>
  </div>
  <div class="form-panel two">
    <div class="form-header">
      <h1>Register </h1>
    </div>
    <div class="form-content">
      <form>
        <div class="form-group">
          <label for="username">Username</label>
          <input type="text" id="username" name="username" required="required"/>
        </div>
        <div class="form-group">
          <label for="password">Password</label>
          <input type="password" id="password" name="password" required="required"/>
        </div>
        <div class="form-group">
          <label for="cpassword">Confirm Password</label>
          <input type="password" id="cpassword" name="cpassword" required="required"/>
        </div>
        <div class="form-group">
          <label for="email">Email Address</label>
          <input type="email" id="email" name="email" required="required"/>
        </div>
        <div class="form-group">
          <button type="submit">Register</button>
        </div>
      </form>
    </div>
  </div>
</div>
html {
  width: 100%;
  height: 100%;
}

body {
/*   background: linear-gradient(90deg, #480048 5%, #C04848 90%);
  background: linear-gradient(90deg, #480048 5%, #C04848 90%); */
  color: rgba(0, 0, 0, 0.6);
  font-family: "Roboto", sans-serif;
  font-size: 14px;
  line-height: 1.6em;
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
}

.overlay, .form-panel.one:before {
  position: absolute;
  top: 0;
  left: 0;
  display: none;
  background: rgba(0, 0, 0, 0.8);
  width: 100%;
  height: 100%;
}

.form {
  z-index: 15;
  position: relative;
  background: #FFFFFF;
  width: 600px;
  border-radius: 4px;
  box-shadow: 0 0 30px rgba(0, 0, 0, 0.1);
  box-sizing: border-box;
  margin: 100px auto 10px;
  overflow: hidden;
}
.form-toggle {
  z-index: 10;
  position: absolute;
  top: 60px;
  right: 60px;
  background: #FFFFFF;
  width: 60px;
  height: 60px;
  border-radius: 100%;
  -webkit-transform-origin: center;
          transform-origin: center;
  -webkit-transform: translate(0, -25%) scale(0);
          transform: translate(0, -25%) scale(0);
  opacity: 0;
  cursor: pointer;
  -webkit-transition: all 0.3s ease;
  transition: all 0.3s ease;
}
.form-toggle:before, .form-toggle:after {
  content: '';
  display: block;
  position: absolute;
  top: 50%;
  left: 50%;
  width: 30px;
  height: 4px;
  background: #4285F4;
  -webkit-transform: translate(-50%, -50%);
          transform: translate(-50%, -50%);
}
.form-toggle:before {
  -webkit-transform: translate(-50%, -50%) rotate(45deg);
          transform: translate(-50%, -50%) rotate(45deg);
}
.form-toggle:after {
  -webkit-transform: translate(-50%, -50%) rotate(-45deg);
          transform: translate(-50%, -50%) rotate(-45deg);
}
.form-toggle.visible {
  -webkit-transform: translate(0, -25%) scale(1);
          transform: translate(0, -25%) scale(1);
  opacity: 1;
}
.form-group {
  display: -webkit-box;
  display: -ms-flexbox;
  display: flex;
  -ms-flex-wrap: wrap;
      flex-wrap: wrap;
  -webkit-box-pack: justify;
      -ms-flex-pack: justify;
          justify-content: space-between;
  margin: 0 0 20px;
}
.form-group:last-child {
  margin: 0;
}
.form-group label {
  display: block;
  margin: 0 0 10px;
  color: rgba(0, 0, 0, 0.6);
  font-size: 12px;
  font-weight: 500;
  line-height: 1;
  text-transform: uppercase;
  letter-spacing: .2em;
}
.two .form-group label {
  color: #FFFFFF;
}
.form-group input {
  outline: none;
  display: block;
  background: rgba(0, 0, 0, 0.1);
  width: 100%;
  border: 0;
  border-radius: 4px;
  box-sizing: border-box;
  padding: 12px 20px;
  color: rgba(0, 0, 0, 0.6);
  font-family: inherit;
  font-size: inherit;
  font-weight: 500;
  line-height: inherit;
  -webkit-transition: 0.3s ease;
  transition: 0.3s ease;
}
.form-group input:focus {
  color: rgba(0, 0, 0, 0.8);
}
.two .form-group input {
  color: #FFFFFF;
}
.two .form-group input:focus {
  color: #FFFFFF;
}
.form-group button {
  outline: none;
  background: #4285F4;
  width: 100%;
  border: 0;
  border-radius: 4px;
  padding: 12px 20px;
  color: #FFFFFF;
  font-family: inherit;
  font-size: inherit;
  font-weight: 500;
  line-height: inherit;
  text-transform: uppercase;
  cursor: pointer;
}
.two .form-group button {
  background: #FFFFFF;
  color: #4285F4;
}
.form-group .form-remember {
  font-size: 12px;
  font-weight: 400;
  letter-spacing: 0;
  text-transform: none;
}
.form-group .form-remember input[type='checkbox'] {
  display: inline-block;
  width: auto;
  margin: 0 10px 0 0;
}
.form-group .form-recovery {
  color: #4285F4;
  font-size: 12px;
  text-decoration: none;
}
.form-panel {
  padding: 60px calc(5% + 60px) 60px 60px;
  box-sizing: border-box;
}
.form-panel.one:before {
  content: '';
  display: block;
  opacity: 0;
  visibility: hidden;
  -webkit-transition: 0.3s ease;
  transition: 0.3s ease;
}
.form-panel.one.hidden:before {
  display: block;
  opacity: 1;
  visibility: visible;
}
.form-panel.two {
  z-index: 5;
  position: absolute;
  top: 0;
  left: 95%;
  background: #4285F4;
  width: 100%;
  min-height: 100%;
  padding: 60px calc(10% + 60px) 60px 60px;
  -webkit-transition: 0.3s ease;
  transition: 0.3s ease;
  cursor: pointer;
}
.form-panel.two:before, .form-panel.two:after {
  content: '';
  display: block;
  position: absolute;
  top: 60px;
  left: 1.5%;
  background: rgba(255, 255, 255, 0.2);
  height: 30px;
  width: 2px;
  -webkit-transition: 0.3s ease;
  transition: 0.3s ease;
}
.form-panel.two:after {
  left: 3%;
}
.form-panel.two:hover {
  left: 93%;
  box-shadow: 0 0 10px rgba(0, 0, 0, 0.2);
}
.form-panel.two:hover:before, .form-panel.two:hover:after {
  opacity: 0;
}
.form-panel.two.active {
  left: 10%;
  box-shadow: 0 0 10px rgba(0, 0, 0, 0.2);
  cursor: default;
}
.form-panel.two.active:before, .form-panel.two.active:after {
  opacity: 0;
}
.form-header {
  margin: 0 0 40px;
}
.form-header h1 {
  padding: 4px 0;
  color: #4285F4;
  font-size: 24px;
  font-weight: 700;
  text-transform: uppercase;
}
.two .form-header h1 {
  position: relative;
  z-index: 40;
  color: #FFFFFF;
}
 


$(document).ready(function() {
  var panelOne = $('.form-panel.two').height(),
    panelTwo = $('.form-panel.two')[0].scrollHeight;

  $('.form-panel.two').not('.form-panel.two.active').on('click', function(e) {
    e.preventDefault();

    $('.form-toggle').addClass('visible');
    $('.form-panel.one').addClass('hidden');
    $('.form-panel.two').addClass('active');
    $('.form').animate({
      'height': panelTwo
    }, 200);
  });

  $('.form-toggle').on('click', function(e) {
    e.preventDefault();
    $(this).removeClass('visible');
    $('.form-panel.one').removeClass('hidden');
    $('.form-panel.two').removeClass('active');
    $('.form').animate({
      'height': panelOne
    }, 200);
  });
});

External CSS

This Pen doesn't use any external CSS resources.

External JavaScript

  1. https://cdnjs.cloudflare.com/ajax/libs/jquery/2.1.3/jquery.min.js