<div class="wrapper">
        <div class="card-switch">
            <label class="switch">
               <input type="checkbox" class="toggle">
               <span class="slider"></span>
               <span class="card-side"></span>
               <div class="flip-card__inner">
                  <div class="flip-card__front">
                     <div class="title">Log in</div>
                     <form class="flip-card__form" action="">
                        <input class="flip-card__input" name="email" placeholder="Email" type="email">
                        <input class="flip-card__input" name="password" placeholder="Password" type="password">
                        <button class="flip-card__btn">Let`s go!</button>
                     </form>
                  </div>
                  <div class="flip-card__back">
                     <div class="title">Sign up</div>
                     <form class="flip-card__form" action="">
                        <input class="flip-card__input" placeholder="Name" type="name">
                        <input class="flip-card__input" name="email" placeholder="Email" type="email">
                        <input class="flip-card__input" name="password" placeholder="Password" type="password">
                        <button class="flip-card__btn">Confirm!</button>
                     </form>
                  </div>
               </div>
            </label>
        </div>   
   </div>
*{
  box-sizing:border-box;
  margin:0;
  padding:0;
}
body {
  height:100vh;
  display:flex;
  align-items:center;
  justify-content:center;
  background-color: #e8e8e8;
  font-family:arial;
}
.wrapper {
  --input-focus: #2d8cf0;
  --font-color: #323232;
  --font-color-sub: #666;
  --bg-color: #fff;
  --bg-color-alt: #666;
  --main-color: #323232;
}
.switch {
  transform: translateY(-200px);
  position: relative;
  display: flex;
  flex-direction: column;
  justify-content: center;
  align-items: center;
  gap: 30px;
  width: 50px;
  height: 20px;
}

.card-side::before {
  position: absolute;
  content: 'Log in';
  left: -70px;
  top: 0;
  width: 100px;
  text-decoration: underline;
  color: var(--font-color);
  font-weight: 600;
}

.card-side::after {
  position: absolute;
  content: 'Sign up';
  left: 70px;
  top: 0;
  width: 100px;
  text-decoration: none;
  color: var(--font-color);
  font-weight: 600;
}

.toggle {
  opacity: 0;
  width: 0;
  height: 0;
}

.slider {
  box-sizing: border-box;
  border-radius: 5px;
  border: 2px solid var(--main-color);
  box-shadow: 4px 4px var(--main-color);
  position: absolute;
  cursor: pointer;
  top: 0;
  left: 0;
  right: 0;
  bottom: 0;
  background-color: var(--bg-colorcolor);
  transition: 0.3s;
}

.slider:before {
  box-sizing: border-box;
  position: absolute;
  content: "";
  height: 20px;
  width: 20px;
  border: 2px solid var(--main-color);
  border-radius: 5px;
  left: -2px;
  bottom: 2px;
  background-color: var(--bg-color);
  box-shadow: 0 3px 0 var(--main-color);
  transition: 0.3s;
}

.toggle:checked + .slider {
  background-color: var(--input-focus);
}

.toggle:checked + .slider:before {
  transform: translateX(30px);
}

.toggle:checked ~ .card-side:before {
  text-decoration: none;
}

.toggle:checked ~ .card-side:after {
  text-decoration: underline;
}

/* card */ 

.flip-card__inner {
  width: 300px;
  height: 350px;
  position: relative;
  background-color: transparent;
  perspective: 1000px;
  text-align: center;
  transition: transform 0.8s;
  transform-style: preserve-3d;
}

.toggle:checked ~ .flip-card__inner {
  transform: rotateY(180deg);
}

.toggle:checked ~ .flip-card__front {
  box-shadow: none;
}

.flip-card__front, .flip-card__back {
  padding: 20px;
  position: absolute;
  display: flex;
  flex-direction: column;
  justify-content: center;
  -webkit-backface-visibility: hidden;
  backface-visibility: hidden;
  background: lightgrey;
  gap: 20px;
  border-radius: 5px;
  border: 2px solid var(--main-color);
  box-shadow: 4px 4px var(--main-color);
}

.flip-card__back {
  width: 100%;
  transform: rotateY(180deg);
}

.flip-card__form {
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 20px;
}

.title {
  margin: 20px 0 20px 0;
  font-size: 25px;
  font-weight: 900;
  text-align: center;
  color: var(--main-color);
}

.flip-card__input {
  width: 250px;
  height: 40px;
  border-radius: 5px;
  border: 2px solid var(--main-color);
  background-color: var(--bg-color);
  box-shadow: 4px 4px var(--main-color);
  font-size: 15px;
  font-weight: 600;
  color: var(--font-color);
  padding: 5px 10px;
  outline: none;
}

.flip-card__input::placeholder {
  color: var(--font-color-sub);
  opacity: 0.8;
}

.flip-card__input:focus {
  border: 2px solid var(--input-focus);
}

.flip-card__btn:active, .button-confirm:active {
  box-shadow: 0px 0px var(--main-color);
  transform: translate(3px, 3px);
}

.flip-card__btn {
  margin: 20px 0 20px 0;
  width: 120px;
  height: 40px;
  border-radius: 5px;
  border: 2px solid var(--main-color);
  background-color: var(--bg-color);
  box-shadow: 4px 4px var(--main-color);
  font-size: 17px;
  font-weight: 600;
  color: var(--font-color);
  cursor: pointer;
}
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