Веб форма авторизации и регистрации на сайте

<div class="cotn_principal">
  <div class="cont_centrar">
    <div class="cont_login">
      <div class="cont_info_log_sign_up">
        <div class="col_md_login">
          <div class="cont_ba_opcitiy">
            <h2>Войти</h2>
            <p>У вас уже есть логин?</p>
            <button class="btn_login" onclick="cambiar_login()">Войти</button>
          </div>
        </div>
        <div class="col_md_sign_up">
          <div class="cont_ba_opcitiy">
            <h2>Регистрация</h2>
            <p>Нет логина?</p>
            <button class="btn_sign_up" onclick="cambiar_sign_up()">Зарегистрироваться</button>
          </div>
        </div>
      </div>
      <div class="cont_back_info">
        <div class="cont_img_back_grey">
          <img src="img/bg.jpg" alt="" />
        </div>
      </div>
      <div class="cont_forms">
        <div class="cont_img_back_">
          <img src="img/bg.jpg" alt="" />
        </div>
        <div class="cont_form_login">
          <a href="#" onclick="ocultar_login_sign_up()"><i class="material-icons">&#xE5C4;</i></a>
          <h2>Войти</h2>
          <input type="text" placeholder="E-mail" />
          <input type="password" placeholder="Пароль" />
          <button class="btn_login" onclick="cambiar_login()">Войти</button>
        </div>
        <div class="cont_form_sign_up">
          <a href="#" onclick="ocultar_login_sign_up()"><i class="material-icons">&#xE5C4;</i></a>
          <h2>Регистрация</h2>
          <input type="text" placeholder="E-mail" />
          <input type="text" placeholder="Логин" />
          <input type="password" placeholder="Пароль" />
          <input type="password" placeholder="Повторите пароль" />
          <button class="btn_sign_up" onclick="cambiar_sign_up()">Зарегистрироваться</button>
        </div>
      </div>
    </div>
  </div>
</div>

.cotn_principal {
  position: absolute;
  width: 100%;
  height: 100%;
  background: #FC466B;  /* fallback for old browsers */
  background: -webkit-linear-gradient(to left, #3F5EFB, #FC466B);  /* Chrome 10-25, Safari 5.1-6 */
  background: linear-gradient(to left, #3F5EFB, #FC466B); /* W3C, IE 10+/ Edge, Firefox 16+, Chrome 26+, Opera 12+, Safari 7+ */
}

.cont_centrar {
  position: relative;
  float: left;
  width: 100%;
}

.cont_login {
  position: relative;
  width: 640px;
  left: 50%;
  margin-left: -320px;
}

.cont_back_info {
  position: relative;
  float: left;
  width: 640px;
  height: 280px;
  overflow: hidden;
  background-color: #fff;
  margin-top: 100px;
  box-shadow: 1px 10px 30px -10px rgba(0, 0, 0, 0.5);
}

.cont_forms {
  position: absolute;
  overflow: hidden;
  top: 100px;
  left: 0px;
  width: 320px;
  height: 280px;
  background-color: #eee;
  -webkit-transition: all 0.5s;
  -moz-transition: all 0.5s;
  -ms-transition: all 0.5s;
  -o-transition: all 0.5s;
  transition: all 0.5s;
}

.cont_forms_active_login {
  box-shadow: 1px 10px 30px -10px rgba(0, 0, 0, 0.5);
  height: 420px;
  top: 20px;
  left: 0px;
  -webkit-transition: all 0.5s;
  -moz-transition: all 0.5s;
  -ms-transition: all 0.5s;
  -o-transition: all 0.5s;
  transition: all 0.5s;
}

.cont_forms_active_sign_up {
  box-shadow: 1px 10px 30px -10px rgba(0, 0, 0, 0.5);
  height: 420px;
  top: 20px;
  left: 320px;
  -webkit-transition: all 0.5s;
  -moz-transition: all 0.5s;
  -ms-transition: all 0.5s;
  -o-transition: all 0.5s;
  transition: all 0.5s;
}

.cont_img_back_grey {
  position: absolute;
  width: 950px;
  top: -80px;
  left: -116px;
}

.cont_img_back_grey>img {
  width: 100%;
  -webkit-filter: grayscale(100%);
  filter: grayscale(100%);
  opacity: 0.7;
  animation-name: animar_fondo;
  animation-duration: 20s;
  animation-timing-function: linear;
  animation-iteration-count: infinite;
  animation-direction: alternate;
}

.cont_img_back_ {
  position: absolute;
  width: 950px;
  top: -80px;
  left: -116px;
}

.cont_img_back_>img {
  width: 100%;
  opacity: 0.8;
  animation-name: animar_fondo;
  animation-duration: 20s;
  animation-timing-function: linear;
  animation-iteration-count: infinite;
  animation-direction: alternate;
}

.cont_forms_active_login>.cont_img_back_ {
  top: 0px;
  -webkit-transition: all 0.5s;
  -moz-transition: all 0.5s;
  -ms-transition: all 0.5s;
  -o-transition: all 0.5s;
  transition: all 0.5s;
}

.cont_forms_active_sign_up>.cont_img_back_ {
  top: 0px;
  left: -435px;
  -webkit-transition: all 0.5s;
  -moz-transition: all 0.5s;
  -ms-transition: all 0.5s;
  -o-transition: all 0.5s;
  transition: all 0.5s;
}

.cont_info_log_sign_up {
  position: absolute;
  width: 640px;
  height: 280px;
  top: 100px;
  z-index: 1;
}

.col_md_login {
  position: relative;
  float: left;
  width: 50%;
}

.col_md_login>h2 {
  font-weight: 400;
  margin-top: 70px;
  color: #fff;
}

.col_md_login>p {
  font-weight: 400;
  margin-top: 15px;
  width: 80%;
  color: #37474F;
}

.btn_login {
  background-color: #03A9F4;
  border: none;
  padding: 10px;
  width: 200px;
  border-radius: 3px;
  box-shadow: 1px 5px 20px -5px rgba(0, 0, 0, 0.4);
  color: #fff;
  margin-top: 10px;
  cursor: pointer;
}

.col_md_sign_up {
  position: relative;
  float: left;
  width: 50%;
}

.cont_ba_opcitiy>h2 {
  font-weight: 400;
  color: #fff;
}

.cont_ba_opcitiy>p {
  font-weight: 400;
  margin-top: 15px;
  color: #fff;
}

/* ----------------------------------
background text
------------------------------------ */

.cont_ba_opcitiy {
  position: relative;
  background-color: rgba(0, 0, 0, 0.5);
  width: 80%;
  border-radius: 3px;
  margin-top: 60px;
  padding: 15px 0px;
}

.btn_sign_up {
  background-color: #d32f2f;
  border: none;
  padding: 10px;
  width: 200px;
  border-radius: 3px;
  box-shadow: 1px 5px 20px -5px rgba(0, 0, 0, 0.4);
  color: #fff;
  margin-top: 10px;
  cursor: pointer;
}

.cont_forms_active_sign_up {
  z-index: 2;
}

@-webkit-keyframes animar_fondo {
  from {
    -webkit-transform: scale(1) translate(0px);
    -moz-transform: scale(1) translate(0px);
    -ms-transform: scale(1) translate(0px);
    -o-transform: scale(1) translate(0px);
    transform: scale(1) translate(0px);
  }
  to {
    -webkit-transform: scale(1.5) translate(50px);
    -moz-transform: scale(1.5) translate(50px);
    -ms-transform: scale(1.5) translate(50px);
    -o-transform: scale(1.5) translate(50px);
    transform: scale(1.5) translate(50px);
  }
}

@-o-keyframes identifier {
  from {
    -webkit-transform: scale(1);
    -moz-transform: scale(1);
    -ms-transform: scale(1);
    -o-transform: scale(1);
    transform: scale(1);
  }
  to {
    -webkit-transform: scale(1.5);
    -moz-transform: scale(1.5);
    -ms-transform: scale(1.5);
    -o-transform: scale(1.5);
    transform: scale(1.5);
  }
}

@-moz-keyframes identifier {
  from {
    -webkit-transform: scale(1);
    -moz-transform: scale(1);
    -ms-transform: scale(1);
    -o-transform: scale(1);
    transform: scale(1);
  }
  to {
    -webkit-transform: scale(1.5);
    -moz-transform: scale(1.5);
    -ms-transform: scale(1.5);
    -o-transform: scale(1.5);
    transform: scale(1.5);
  }
}

@keyframes identifier {
  from {
    -webkit-transform: scale(1);
    -moz-transform: scale(1);
    -ms-transform: scale(1);
    -o-transform: scale(1);
    transform: scale(1);
  }
  to {
    -webkit-transform: scale(1.5);
    -moz-transform: scale(1.5);
    -ms-transform: scale(1.5);
    -o-transform: scale(1.5);
    transform: scale(1.5);
  }
}

.cont_form_login {
  position: absolute;
  opacity: 0;
  display: none;
  width: 320px;
  -webkit-transition: all 0.5s;
  -moz-transition: all 0.5s;
  -ms-transition: all 0.5s;
  -o-transition: all 0.5s;
  transition: all 0.5s;
}

.cont_forms_active_login {
  z-index: 2;
}

.cont_forms_active_login>.cont_form_login {}

.cont_form_sign_up {
  position: absolute;
  width: 320px;
  float: left;
  opacity: 0;
  display: none;
  -webkit-transition: all 0.5s;
  -moz-transition: all 0.5s;
  -ms-transition: all 0.5s;
  -o-transition: all 0.5s;
  transition: all 0.5s;
}

.cont_form_sign_up>input {
  text-align: left;
  padding: 15px 5px;
  margin-left: 10px;
  margin-top: 20px;
  width: 260px;
  border: none;
  color: #fff;
}

.cont_form_sign_up>h2 {
  margin-top: 50px;
  font-weight: 400;
  color: #fff;
}

.cont_form_login>input {
  padding: 15px 5px;
  margin-left: 10px;
  margin-top: 20px;
  width: 260px;
  border: none;
  text-align: left;
  color: #fff;
}

.cont_form_login>h2 {
  margin-top: 110px;
  font-weight: 400;
  color: #fff;
}

.cont_form_login>a, .cont_form_sign_up>a {
  color: #fff;
  position: relative;
  float: left;
  margin: 10px;
  margin-left: 30px;
}

function cambiar_login() {
  document.querySelector('.cont_forms').className = "cont_forms cont_forms_active_login";
  document.querySelector('.cont_form_login').style.display = "block";
  document.querySelector('.cont_form_sign_up').style.opacity = "0";

  setTimeout(function() {
    document.querySelector('.cont_form_login').style.opacity = "1";
  }, 400);

  setTimeout(function() {
    document.querySelector('.cont_form_sign_up').style.display = "none";
  }, 200);
}

function cambiar_sign_up(at) {
  document.querySelector('.cont_forms').className = "cont_forms cont_forms_active_sign_up";
  document.querySelector('.cont_form_sign_up').style.display = "block";
  document.querySelector('.cont_form_login').style.opacity = "0";

  setTimeout(function() {
    document.querySelector('.cont_form_sign_up').style.opacity = "1";
  }, 100);

  setTimeout(function() {
    document.querySelector('.cont_form_login').style.display = "none";
  }, 400);

}

function ocultar_login_sign_up() {

  document.querySelector('.cont_forms').className = "cont_forms";
  document.querySelector('.cont_form_sign_up').style.opacity = "0";
  document.querySelector('.cont_form_login').style.opacity = "0";

  setTimeout(function() {
    document.querySelector('.cont_form_sign_up').style.display = "none";
    document.querySelector('.cont_form_login').style.display = "none";
  }, 500);

}