<div class="container">
  <h1 class="animatable" id="title">Woodwoerk</h1>
  <div class="animatable" id="message"></div>
  <div class="animatable" id="sun"></div>

  <div class="form animatable">
    <div class="content signup--content">
      <div class="sign--type">
        <span>Already have an account?<br></span>
        <span class="link signin"><a href="#signin">Sign in</a></span>
      </div>

      <form id="signed-up" enctype="multipart/form-data">
        <div class="spacer"></div>
        <input type="email" name="email" id="email" class="text-box" required="required" placeholder="Enter your email" value="example@email.com">
        <input type="password" name="password" id="password" class="text-box" required="required" placeholder="Enter your password" value="password">
        <input type="password" name="password" id="password" class="text-box" required="required" placeholder="Confirm your password" value="password">
        <input type="submit" value="Sign up" class="submit">
      </form>
    </div>

    <div class="content signin--content">
      <div class="sign--type">
        <span>Don't have an account?<br></span>
        <span class="link signup"><a href="#signup">Sign Up</a></span>
      </div>

      <form id="signed-in" enctype="multipart/form-data">
        <div class="spacer"></div>
        <input type="email" name="email" id="email" class="text-box" required="required" placeholder="Email" value="example@email.com">
        <input type="password" name="password" id="password" class="text-box" required="required" placeholder="Password" value="password">
        <input type="submit" value="Sign in" class="submit">
      </form>
    </div>
  </div>
</div>
@import url(https://fonts.googleapis.com/css?family=Cantarell|Josefin+Sans);

$font-head: 'Josefin Sans', sans-serif;
$font-copy: 'Cantarell', sans-serif;

//Colors
$body-bg: #17BEBB;
$primary: #26547C;
$bg: #F5F5F5;

* {
  box-sizing: border-box;
  transition: all 0.4s cubic-bezier(0.4, 0, 0.2, 1);
}

body {
  font-family: $font-copy;
  background-color: $body-bg;
  color: rgba(0,0,0,0.85);
  font-size: 16px;
  overflow: hidden;  
}

a {
  font-size: 90%;
  cursor: pointer;
  letter-spacing: 2px;
  text-decoration: none;
  border-bottom: 1px solid rgba(211,49,68,0.8);
  box-shadow: 0 0 0 $bg, 0 0 0 rgba(211,49,68,0.8);
  text-transform: uppercase;
  color: rgba(211,49,68,0.8);
  transition: all 0.2s;
}
a:hover {
  border-bottom: 2px solid rgba(211,49,68,0.7);
  box-shadow: 0 2px 0 $bg, 0 4px 0 rgba(211,49,68,0.7);
  color: rgba(211,49,68,1);
  transition: all 0.1s;
}


#title {
  font-size: 110%;
  margin-bottom: 23px;
  text-align: center;
  letter-spacing: 10px;
  text-indent: 10px;
  text-transform: uppercase;
  font-weight: normal;
  color: $bg;
  text-shadow: 0px 0px 0px rgba(255,255,255,0);
  z-index: -20;

  font-family: $font-head;
}
#title.signed-in{
  text-shadow: 0px 0px 40px rgba(255,255,255,1), 0 -5px 6px rgba(0,0,0,0.3);
  font-size: 180%;
  letter-spacing: 20px;
  transform: translateY(85px);
  transition: all 2.5s, text-shadow 4s 1s;
}
#title.signed-up{
  text-shadow: 0px 0px 40px rgba(255,255,255,1);
  font-size: 200%;
  letter-spacing: 20px;
  transform: translateY(160px);
  transition: all 1s, text-shadow 4s 1s;
}

#message {
  position: absolute;
  text-align: center;
  left: 40px; right: 40px;
  font-size: 115%;
  letter-spacing: 10px;
  color: $bg;
  opacity: 0;
  top: 40%;
  text-shadow: 0 0 0 rgba(0,0,0,0.4);
  z-index: -2;
}
#message.signed-in {
  opacity: 1;
  top: 290px;
  font-size: 120%;
  letter-spacing: 8px;
  text-shadow: 0 5px 6px rgba(0,0,0,0.3);

  transition: all 2s 0.5s, opacity 1s 0.5s, text-shadow 4s 1s;
}
#message.signed-up {
  opacity: 1;
  top: 200px;
  letter-spacing: 8px;
  z-index: 11;

  transition: all 2s 0.5s, opacity 1s 1.5s;
}

.content {
  display: flex;
  flex-direction: column;
}

.container {
  text-align: center;
  position: relative;
  overflow: hidden;  
  /* this fixes the overflow:hidden bug */

  width: 600px;
  height: 600px;
  background-color: $primary;
  box-shadow: rgba(0, 0, 0, 0.5) 0px 10px 30px, rgba(0,0,0,0.4) 0px 0px 200px;
  z-index: 1;

  border-radius: 50%;
  margin: calc(50vh - 300px) 0 0 calc(50vw - 300px);
  padding: 40px 40px 0 40px;
}
.container.signed-up{
  background-color: #482C3D;
  transition: all 1s;

  animation: sky-color 5s ease;
}

.form{
  padding: 50px;
  background-color: $bg;
  width: 100%;
  height: 100%;
  z-index: 10;
  border-radius: 50%;

  box-shadow: 0px 0px 0px 0px rgba(100,100,100,0), 0px 0px 0px 0px rgba(100,100,100,0);
}

.form.signed-in{
  background-color: $bg;
  transform: translateY(100%) rotate(90deg) scale(2, 2);
  box-shadow: 0px 100px 0px 20px rgba(1,1,1,0.3), -30px -90px 0px 5px rgba(1,1,1,0.2);

  transition: all 0.6s cubic-bezier(0.4, 0, 0.2, 1), box-shadow 2s 1s;
}

.form.signed-up{
  background-color: $bg;
  transform: translateY(100%) rotate(90deg) scale(2, 2);
  box-shadow: 0px 70px 0px 10px rgba(255,255,255,0.3), -10px -70px 0px 5px rgba(255,255,255,0.2);

  transition: all 0.6s cubic-bezier(0.4, 0, 0.2, 1), box-shadow 2s 1s;
}

form {
  margin: 0 auto;
  width: 70%;
  height: 300px;
}

input:-webkit-autofill {
    -webkit-box-shadow: 0 0 0px 1000px $bg inset;
}

.sign--type {
  animation: slideUp 0.8s cubic-bezier(0.37, 0.82, 0.2, 1);
}
input:first-of-type {
  animation: slideUp 0.8s cubic-bezier(0.37, 0.82, 0.2, 1) 0.1s;
}
 input:nth-of-type(2) {
  animation: slideUp 0.8s cubic-bezier(0.37, 0.82, 0.2, 1) 0.2s;
}
 input:nth-of-type(3) {
  animation: slideUp 0.8s cubic-bezier(0.37, 0.82, 0.2, 1) 0.3s;
}
 input:nth-of-type(4) {
  animation: slideUp 0.8s cubic-bezier(0.37, 0.82, 0.2, 1) 0.4s;
}

#sun{
  position: absolute;
  width: 120px;
  height: 120px;
  left: 50%; 
  margin-left: -60px;
  border-radius: 50%;
  background-color: #FFDD59;
  box-shadow:  0 0 10px #FFDD59, 0 0 50px yellow;
  margin-top: 60%;
  z-index: -1;

  transition: all cubic-bezier(.87,-.41,.19,1.44) 0.4s;
}
#sun.signed-in{
  margin-top: 10%;
  background-color: #FFDD59;
  box-shadow: 0 0 10px #FFDD59, 0 0 50px yellow;
  z-index: -1;

  transition: all 2s cubic-bezier(.84,.33,.37,1.42) 0.5s;
}
#sun.signed-up{
  box-shadow:  0 0 10px #D8973C, 0 0 50px yellow;
  background-color: #FFBB00;
  animation: sunny 4s linear;
}

.spacer{
  display: block;
  width: 100%;
  height: 40px;
  background-color: transparent;
}
input.text-box {
  font-size: 90%;
  display: block;
  width: 100%;
  height: 42px;
  margin-bottom: 12px;
  padding: 16px 13px;
  color: rgba(0,0,0,0.65);
  border: 1px solid rgba(0,0,0,0.15);
  background: rgba(0,0,0,0);
  border-radius: 2px;
}
input.text-box::-webkit-input-placeholder {
  font-size: 90%;
  color: rgba(0,0,0,0.4);
}
input.text-box:focus {
  border-color: rgba(211,49,68,0.5);
}
input.submit {
  font-size: 100%;
  line-height: 16px;
  display: block;
  width: 100%;
  height: 42px;
  cursor: pointer;
  vertical-align: middle;
  letter-spacing: 2px;
  text-transform: uppercase;
  color: rgba(255,255,255,1);
  border: 0 solid rgba(0,0,0,0.8);
  background: $body-bg;
  margin-top: 0px;

  box-shadow: 0 2px 0 $bg, 0 6px 0 $body_bg;

  transition: all 0.4s;
}
input.submit:hover {
  background: $primary;
  box-shadow: 0 2px 0 $bg, 0 6px 0 $primary, 0 8px 0 $bg, 0 11px 0 $primary;
  margin-top: -2px;
  transition: all 0.2s;
}
input.submit:active{
  transition: all 0.1s;
  margin-top: 15px;
  box-shadow: 0 0px 0 $bg, 0 3px 0 $primary, 0 0px 0 $bg, 0 6px 0 $primary;
} 

input:focus {
  outline: none;
}
.submit-wrap {
  position: absolute;
  bottom: 0;
  width: 100%;
}
.signup--content {
  display: none;
}
.sign--type{
  padding: 0;
  opacity: 0.8;
}

@keyframes slideUp {
  0% {
    opacity: 0;
    margin-top: 100%;
  }
  100% {
    opacity: 1;
    margin-top: 0%;
  }
}


@keyframes sunny {
  from {
    margin-top: 30%;
    margin-left: -60px;
    transform: rotate(-90deg)
               translate(-200px)
               rotate(90deg);
  }
  to {
    margin-top: 30%;
    margin-left: -60px;
    transform: rotate(270deg)
               translate(-200px) 
               rotate(-270deg);
  }
}

@keyframes sky-color {
  0%{
      background-color: $primary;
  }
  5% {
      background-color: #482C3D;
  }
  50%{
      background-color: #258EA6;
  }
  100%{
      background-color: #482C3D;
  }
}
View Compiled
var content = $('.content'),
  form = $('.form'),
  message = $('#message'),
  animatable = $('.animatable'),
  signedIn = 'signed-in',
  signedUp = 'signed-up';

//Toggle between forms
$('.sign--type .link').click(function() {
  content.hide();
  if ($(this).hasClass('signin')) {
    $('.signin--content').show();
  } 
  else if ($(this).hasClass('signup')) {
    $('.signup--content').show();
  }
});

//On form submit
$('form').submit(function () {
  sendForm($(this).attr('id'));
  return false;
});

//Animate form and wait for reset
function sendForm(form) {
  setTimeout(function() {
    animateForm(form);
  }, 200);
  setTimeout(reset, 5000);
}

function animateForm(frm) {
  animatable.addClass(frm);
  content.hide(300);

  //check which form to call appropriate animation
  if (frm == signedIn) {
    message.text("welcome back");
  } else if (frm == signedUp) {
    message.text("welcome to")
    $('.container').addClass(signedUp);
  }
}

//reset form
function reset() {  
  content.hide();
  if (form.hasClass(signedIn)) {
    $('.signin--content').show();
    animatable.removeClass(signedIn);
  }
  if (form.hasClass(signedUp)) {
    $('.signup--content').show();
    animatable.removeClass(signedUp);
    $('.container').removeClass(signedUp);
  }
  message.text(null);
}

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