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CSS

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JavaScript

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HTML 

              
                <form class="form registerform" autocomplete="off" novalidate="">
  <legend>Simple CSS Form Validation</legend>
	  <div class="FormItem NameItem">
      <input type="text" id="name" name="name" placeholder="Name" maxlength=”20” class="formInput" required />
      <span class="validation"> OK </span>
  </div>
  <div class="FormItem PassItem">
      <input type="password" id="password" name="password" placeholder="Password" class="formInput" required pattern="(?=.*\d)(?=.*[a-z])(?=.*[A-Z]).{6,}" />
      <span class="validation"> OK </span>
  </div>
  <div class="FormItem EmailItem">
  <input type="email" placeholder="Enter your email address" tabindex="1" class="formInput newsletter-email" required>
    <span class="validation"> OK </span>
	  <!--<input type="submit" value="OK" tabindex="2" class="validation newsletter-submit"> -->
  </div>
</form>
<p class="Explanations">
  JS optional to check the validation on focusout. <br /> Can be uncommented.
  </p>
!

CSS 

              
                * {
  box-sizing: border-box;
  margin: 0;
  padding: 0;
  border: 0;
  box-shadow: none;
  outline: none;
}
input:focus, textarea:focus, select:focus { background-color: #ddd; box-shadow: 0 0 0.75em #FF0404; border: 0 none; color: #080808; }
input:focus:valid { box-shadow: 0 0 0.75em green;}
::-webkit-input-placeholder  { color:#676767; transition:all 0.333s ease-in-out; }
::-moz-placeholder {color: #676767;opacity: 1; transition:all 0.333s ease-in-out; }
:-moz-placeholder { color:#676767; opacity: 1; transition:all 0.333s ease-in-out; }
:-ms-input-placeholder {color: #676767; -ms-transition: all 0.2s ease;}
[placeholder]:focus::-webkit-input-placeholder { transition: text-indent 0.15s 0.15s ease; text-indent: -200%; opacity: 1; }

body {
  background:rgb(75, 121, 207);
  color: #252525;
  font-family: "Roboto", Helvetica, Arial, "Lucida Grande", sans-serif;
  font-size:16px;
  padding:0.5rem;
  transition:none;
  background:linear-gradient(270deg, rgb(71, 74, 51), rgb(100, 105, 47), rgb(143, 129, 63));
  background-size: 300% 400%;
}  


.form {
  display: block;
  position: relative;
  max-width: 400px;
  margin: 2rem auto;
  font-size:1.5rem;
}

input {
  font: 1em "Roboto", Helvetica, Arial, "Lucida Grande", sans-serif;
  font-weight: 300;
  padding: 1rem;
}

.FormItem {
  display:inline-block; width:100%; margin: 0.5em auto 0.5em; position:relative; font-size:1em;
}

.formInput {
  display: block;
  width: 100%;
  padding-right: 3rem;
  box-sizing:border-box;
}
.validation { width:2.75em; height:4rem; background:#CCC; padding:0; margin:0; line-height:4rem; text-align:center; font-weight:normal;
  font-family: "Roboto", Helvetica, Arial, "Lucida Grande", sans-serif;
  position: absolute;
  top: 0;
  right: 0;
  opacity: 0;
  pointer-events: none;
  transition: all 0.25s ease 0.125s;
  cursor:not-allowed;
  width:2.75em;
  color:transparent;
  
}
.newsletter-submit{}
.formInput.empty + .validation,
.formInput:focus:invalid + .validation,
.formInput:active:invalid + .validation {
  opacity: 1;
  background-color: red;
  color:transparent;
  transition: none;
}
.formInput.empty + .validation:after,
.formInput:focus:invalid + .validation:after,
.formInput:invalid + .validation:after {
  display:block;
  content: "!";
  color:yellow;
  position:absolute;
  right:0;
  top:0;
  width:100%;
  height:auto;
  font-weight:bold;
  text-shadow:2px 2px 3px #333, 3px 3px 3px #111;
  font-size:2em;
  line-height:1.286em;
  z-index:999;
}
.formInput:valid + .validation {
  opacity: 1;
  color: #fff;
  background-color: #4CD964;
  pointer-events: auto;
  cursor:default;
}

.Explanations { color:#FFF; font-size:1.333rem; text-align:center; display:block; margin:1em auto;}
!

JS 

              
                // with JS --> Osvaldas Valutis, http://osvaldas.info/minimalist-newsletter-subscription-form

// NO JS --> https://www.designernews.co/users/8690/dan-klammer
// https://output.jsbin.com/teney

/*
$('input').keyup(function() {
    if( $(this).val() == ""){
        $(this).addClass("empty");
    }else{
        $(this).removeClass("empty");
    }
}).focusout(function() {
    if( $(this).val() == "" || $(this).isValid() ){
        $(this).addClass("empty");
    }else{
        $(this).removeClass("empty");
    }
}); 
*/
!
999px

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