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HTML 

              
                <div class="form" id="loginform">
    <h1> Login </h1>
    <form novalidate>
        <p class="email">
            <label for="email">Email login <span>*</span>
            </label>
            <input class="input" required type="email" id="email" name="email" pattern="@"/>
          <span class="validation error"> Please enter a valid email</span>
          <span class="validation req"> This field is required</span>
        </p>
        <p class="password">
            <label for="password">Password <span>*</span></label>
            <input class="input" required type="password" id="password" name="password" />
          <span class="validation req"> This field is required</span>
        </p>
      <p class="remember">
        <input class="checkbox" type="checkbox" id="remember"/>
        <label for="remember"> Remember me</label>
        
      </p>
      <p class="login">
        <input type="submit" value="Login" />
      </p>
    </form>
</div>
!

CSS 

              
                @primary : #FEDC2A ;
@complementary :#5A3B5D;
@lightsep: rgb(220, 220, 220);


/*** Note: I put the animation first in the CSS and all the "page styling under, but you might want to do that on real projects and respect the cascade. 

Also for the purpose of the demo during the conference I'm using .checked but normaly you could your [type="checkbox"] to target the checkbox 
Also note that  ***/


/****** 1. We can do nice things with :checked ******/


/* let's animate the transition on the checkbox background */

/* "normal" state */
.checkbox + label:before {
    background: rgb(255, 255, 255);
    border: 1px solid rgb(216, 216, 216);
}

/* transitionned state when checked */
.checkbox:checked + label:before {
    background: @complementary;
    border-color: @complementary;
}

/* applying transition */
.checkbox + label:before {
    transition: 
      background .2s, 
      border-color .2s;
    /* double transition, yup ! */  
}



/* Let's animate the mark */
.checkbox:not(:checked) + label:after {
    transform: scale(0);
}
.checkbox:checked + label:after {
    transform: scale(1);
}
.checkbox + label:after {
    transition: transform .4s;
}



/****** 2. Let's shake this form  ******/

/* Creating the animation */
@keyframes shakeMe {
    0%, 100% {
        transform: translateX(0);
    }
    20%,
    60% {
        transform: translateX(-10px);
    }
    40%,
    80% {
        transform: translateX(10px);
    }
}


/* Applying the animation */
.errors {
    animation-name: shakeMe;
    animation-duration: .5s;
}




/****** Here come the unicorns, aka all the styling not useful for the animation demo at the conference :)  ******/

 body {
    background: #FEDC2A;
    font-family: 'Raleway', sans-serif;
    background-size: cover;
    min-height: 100vh;
    display: flex;
    align-items: center;
    justify-content: center;
}


.form {
    background: #fff;
    border: 1px solid #D9D9D9;
    color: rgb(99, 99, 99);
    width: 300px;
    border-radius: 4px;
    margin: 0 auto;
    padding: 20px 30px;
    h1 {
        text-transform: uppercase;
        font-weight: normal;
        font-size: 1.5em;
        text-align: center;
        margin: 0;
        padding: 10px 0px;
        border-bottom: 1px solid     @lightsep;
    }
}

form p {
    position: relative;
    margin: 25px 0 10px 0 ;
    position: relative;
}


p.remember {
    padding-bottom: 20px;
    margin-bottom: 20px;
    border-bottom: 1px solid @lightsep;
}
.email label,
.password label,
.input {
    display: block;
    width: 100%;
    padding-bottom: 10px;
    box-sizing: border-box;
}


/* Submit button Styling */

[type="submit"] {
    display: block;
    color: @complementary;
    font-weight: bold;
    border-radius: 2px;
    background: @primary;
    box-shadow: 5px 5px 0 0 @primary,
      inset 4px 4px 0 0 white;
    border: 2px solid @complementary; 
    border-radius: 3px;
    padding: 10px;
    width: 100%;
    margin: 0 auto;
    transition: background .3s;
    &:hover {
        background: white;
    box-shadow: 5px 5px 0 0 @primary,
      inset 4px 4px 0 0 white;
    }
  
    &:active,
    &:focus {
       /* position: relative;
        top: 1px; */
        // outline: none;
       //  background: darken(@primary, 10%);
    }
}

[type="password"],
[type="email"] {
    padding: 20px;
    &:focus {
        outline: none;
    }
}
/* Styling the input */

.input {
    font-size: .85em;
    background: rgb(255, 255, 255);
    border: 1px solid @lightsep;
    height: 40px;
    transition: border-color .4s, box-shadow 1s;
}

.input:active,
.input:focus {
    border: 1px solid @complementary;
    box-shadow: 4px 4px 0 #C7A9CD;
}


/* Removing the checkbox from screen */
.checkbox {
    position: absolute;
    left: -300%;
}
.checkbox + label {
    position: relative;
    padding-left: 25px;
    cursor: pointer;
}

/* Creating the fake checkbox */
.checkbox + label:before {
    content: '';
    position: absolute;
    left: 0;
    top: 0;
    width: 15px;
    height: 15px;
    border-radius: 2px;
}

/* accessibility */
.checkbox:focus + label:before {
    border: 1px solid @complementary;
    box-shadow: 4px 4px 0 #C7A9CD;
}

/* Adding the SVG mark */

.checkbox + label:after {
    content: " ";
    background: url('data:image/svg+xml;utf8,<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 10.7 8.7" enable-background="new 0 0 10.7 8.7"><path fill="white" d="M4.2 8.7c-.3 0-.5-.3-.7-.5l-3.2-3.1c-.4-.4-.4-1.1 0-1.5s1-.4 1.4 0l2.4 2.3 4.9-5.6c.4-.4 1-.5 1.4-.1.4.4.5 1 .1 1.4l-5.6 6.6c-.1.2-.4.5-.7.5z"/></svg>') no-repeat; /* OMG you can embed SVG in background, awesoome */
    position: absolute;
    left: 2px;
    top: 3px;
    width: 13px;
    height: 13px;
}



/****** Validation messages ******/

.invalid {
    border-color: rgb(183, 0, 76);
}

.required {
    border-color: #B54300;
}

.validation {
  display: block;
  font-size: .8em;  
  padding-top: .5em;
  position: absolute;
  right:0;
  opacity: 0;
  transition: opacity 1s ;
}

.validation.req {
  color: #B54300;
}

.validation.error {  
  color: rgb(183, 0, 76); 
}


.invalid:not(.required)  ~ .validation.error {
  opacity: 1;
  transform: scale(1);   
}

.required  ~ .validation.req {
  opacity: 1;
  transform: scale(1);   
}
!

JS 

              
                /* JavaScript with the precious help of Jean Pierre Vincent @theystolemynick https://twitter.com/theystolemynick  */

function validateThisField (field) {
	if (field.required && field.value === '') {
		field.classList.add('required');
		formIsValid = false;
	}
	if (field.pattern
			&& !(new RegExp(field.pattern).exec(field.value) !== null) ) {
		field.classList.add('invalid');
		formIsValid = false;
	}

}

var form = document.getElementById('loginform');
var fields = form.querySelectorAll('input');
var formIsValid = true;

form.addEventListener('submit', function (e) {
	e.preventDefault();
	Array.prototype.forEach.call(fields, validateThisField);
  	// also have a global state on the form
	if (!formIsValid) {
    form.classList.remove('errors');
        setTimeout(function() {form.classList.add('errors');}, 0);
    }
});
/*
 form.addEventListener('focus', function (e) {
	e.target.classList.remove('required');
	e.target.classList.remove('invalid');
}, true); */

form.addEventListener('blur', function (e) {
  e.target.classList.remove('required');
	e.target.classList.remove('invalid');
	validateThisField(e.target);
}, true);
!
999px

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