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CSS

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JavaScript

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HTML 

              
                <form action="#" class="form">
    <div class="form-group">
      <label for="name">Nombre *</label>
      <input type="text" class="form-input" id="name" placeholder="Introduce tu nombre" minlength="3" required>
    </div>
    <div class="form-group">
      <label for="surname">Apellidos</label>
      <input type="text" class="form-input" id="surname" placeholder="Introduce tus apellidos">
    </div>
    <div class="form-group">
      <label for="birthdate">Fecha de nacimiento *</label>
      <input type="text" class="form-input" id="birthdate" placeholder="Introduce tu fecha de nacimiento" aria-label="Utiliza el formato DD/MM/AAAA" title="Formato DD/MM/AAAA" pattern="^(0?[1-9]|[12]\d|3[01])[\/](0?[1-9]|1[0-2])[\/](19|20)\d{2}$" required>
    </div>
    <div class="form-group">
      <label for="email">Email *</label>
      <input type="email" class="form-input" id="email" placeholder="Introduce tu email" required>
    </div>
    <div class="form-group">
      <label for="favouriteNumber">Número favorito *</label>
      <input type="number" class="form-input" id="favouriteNumber" placeholder="Introduce tu número favorito" min="0" max="999" required>
    </div>
    <div class="form-group">
      <label for="comment">Comentario *</label>
      <textarea class="form-input form-input--textarea" id="comment" rows="3" placeholder="Deja tu comentario" required></textarea>
    </div>
    <div class="form-group form-group--submit">
      <button class="form-button" type="submit">Enviar</button>
    </div>
  </form>
!

CSS 

              
                $c-white: #fff;
$c-black: #333;

$c-border: #e8e8e8;
$c-placeholder: #999;
$c-error: red;
$c-success: #2fe678;

$c-primary: #02ffd0;
$c-primary-hover: #80fee7;

* {
  box-sizing: border-box;
  font-family: Courier;
}

%formInput {
	display: block;
	width: 100%;
	height: 40px;
	border: 1px solid $c-border;
	border-radius: 4px;
	padding: 10px 16px;
	box-shadow: 1px 1px 2px 0 rgba($c-black, 0.2) inset;
	background-color: $c-white;
	background-clip: padding-box;
	color: $c-placeholder;
	font-size: 16px;
	font-weight: normal;
	transition: all 250ms;

	// Placeholder
	&::placeholder {
		color: $c-placeholder;
	}

	// Focus
	&:focus:required {
		border-color: $c-primary;
		outline: 0 none;
	}

	// States
	&:required:placeholder-shown {
		border: 1px solid $c-border;
	}
	&:required:not(:placeholder-shown):invalid {
		border: 1px solid $c-error;
		color: $c-error;
		box-shadow: 0 0 0 1px;
	}
	&:required:not(:placeholder-shown):valid {
		border: 1px solid $c-success;
		color: $c-success;
		box-shadow: 0 0 0 1px;    
	}
  &:required:focus:invalid {
		border: 1px solid $c-error;
		color: $c-error;
		box-shadow: 0 0 0 1px;
	}
}

.form {
  max-width: 30rem;
  margin: 2rem auto;
	&-group {
		margin-bottom: 24px;

		label {
			display: block;
			margin-bottom: 6px;
			font-weight: bold;
		}

		// MODIFIERS
		&--submit {
			display: flex;
			justify-content: flex-end;
		}
	}

	&-input {
		@extend %formInput;

		// Disabled
		&:disabled {
			opacity: 0.7;
			cursor: not-allowed;
		}
	}
  
  &-button {
    padding: 1.5rem 2rem;
    font-size: 1.125rem;
    cursor: pointer;
    background-color: $c-primary;
    border: 0;
    border-radius: 0.125rem;
    transition: background-color 300ms;
    
    &:hover, 
    &:focus {
      background-color: $c-primary-hover;
    } 
  }

	// MODIFIERS
	textarea {
		&.form-input {
			height: 20rem;
			resize: none;
		}
	}
}
!

JS
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999px

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