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CSS

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HTML 

              
                <label class="custom-field">
  <input type="email" placeholder="&nbsp;"/>
  <span class="placeholder">Enter Email</span>
  <span class="error-message" aria-live="polite">The email is invalid</span>
  </label>

<label class="custom-field one">
  <input type="text" placeholder=" "/>
  <span class="placeholder">Enter Text</span>
</label>

<label class="custom-field two">
  <input type="url" placeholder="&nbsp;"/>
  <span class="placeholder">Enter URL</span>
</label>

<label class="custom-field three">
  <input type="password" placeholder="&nbsp;"/>
  <span class="placeholder">Enter Password</span>
  <span class="border"></span>
</label>

<a href="https://youtu.be/3AK3vspZvvM" style="position: fixed; bottom: 25px; left: 25px; color: #222; text-shadow: 0 0 1px #222;" target="_blank">Watch Video Explanation</a>
!

CSS 

              
                /* Video Explanation - https://youtu.be/3AK3vspZvvM */
body {
  width: 100vw;
  height: 100vh;
  display: flex;
  flex-direction: column;
  justify-content: center;
  align-items: center;
  font-family: sans-serif;
  font-size: 16px;
}

*, *::before, *::after {
  box-sizing: border-box;
}

.custom-field {
  position: relative;
  font-size: 14px;
  border-top: 20px solid transparent;
  margin-bottom: 5px;
  display: inline-block;
  --field-padding: 12px;
}

.custom-field input {
  border: none;
  -webkit-appearance: none;
  -ms-appearance: none;
  -moz-appearance: none;
  appearance: none;
  background: #f2f2f2;
  padding: var(--field-padding);
  border-radius: 3px;
  width: 250px;
  outline: none;
  font-size: 14px;
}

.custom-field .placeholder {
  position: absolute;
  left: var(--field-padding);
  width: calc(100% - (var(--field-padding) * 2));
  overflow: hidden;
  white-space: nowrap;
  text-overflow: ellipsis;
  top: 22px;
  line-height: 100%;
  transform: translateY(-50%);
  color: #aaa;
  transition: 
    top 0.3s ease,
    color 0.3s ease,
    font-size 0.3s ease;
}

.custom-field input.dirty + .placeholder,
.custom-field input:focus + .placeholder,
.custom-field input:not(:placeholder-shown) + .placeholder {
  top: -10px;
  font-size: 10px;
  color: #222;
}

.custom-field .error-message {
  width: 100%;
  display: flex;
  align-items: center;
  padding: 0 8px;
  font-size: 12px;
  background: #d30909;
  color: #fff;
  height: 24px;
}

.custom-field .error-message:empty {
  opacity: 0;
}

/* ONE */
.custom-field.one input {
  background: none;
  border: 2px solid #ddd;
  transition: border-color 0.3s ease;
}

.custom-field.one input + .placeholder {
  left: 8px;
  padding: 0 5px;
}

.custom-field.one input.dirty,
.custom-field.one input:not(:placeholder-shown),
.custom-field.one input:focus {
  border-color: #222;
  transition-delay: 0.1s
}

.custom-field.one input.dirty + .placeholder,
.custom-field.one input:not(:placeholder-shown) + .placeholder,
.custom-field.one input:focus + .placeholder {
  top: 0;
  font-size: 10px;
  color: #222;
  background: #fff;
  width: auto
}

/* TWO */
.custom-field.two input {
  border-radius: 0;
  border-top-left-radius: 3px;
  border-top-right-radius: 3px;
  background:
    linear-gradient(90deg, #222, #222) center bottom/0 0.15em no-repeat,
    linear-gradient(90deg, #ccc, #ccc) left bottom/100% 0.15em no-repeat,
    linear-gradient(90deg, #fafafa, #fafafa) left bottom/100% no-repeat;
  transition: background-size 0.3s ease;
}

.custom-field.two input.dirty,
.custom-field.two input:not(:placeholder-shown),
.custom-field.two input:focus {
  background-size: 100% 0.15em, 100% 0.1em, 100%;
}

/* THREE */
.custom-field.three {
  --draw-duration: 0.1s;
  --draw-color: #222;
  --draw-line-width: 2px;
  --draw-easing: linear;
}

.custom-field.three .border {
  width: 100%;
  height: 100%;
  position: absolute;
  left: 0;
  top: 0;
  transform: none;
  display: flex;
  align-items: center;
  padding-left: 12px;
  borde-radius: 3px;
}

.custom-field.three .border::after, 
.custom-field.three .border::before {
  content: "";
  width: 0;
  height: 0;
  display: inline-block;
  position: absolute;
  border-radius: 3px;
}

.custom-field.three .border::before {
  left: 0;
  bottom: 0;
  border-right: 0px solid var(--draw-color);
  border-bottom: 0px solid var(--draw-color);
  transition: 
    border 0s linear calc(var(--draw-duration) * 4),
    height var(--draw-duration) var(--draw-easing) calc(var(--draw-duration) * 2),
    width var(--draw-duration) var(--draw-easing) calc(var(--draw-duration) * 3);
}

.custom-field.three .border::after {
  right: 0;
  top: 0;
  border-left: 0px solid var(--draw-color);
  border-top: 0px solid var(--draw-color);
  transition: 
    border 0s linear calc(var(--draw-duration) * 2),
    height var(--draw-duration) var(--draw-easing),
    width var(--draw-duration) var(--draw-easing) var(--draw-duration);
}

.custom-field.three input:focus ~ .border::before,
.custom-field.three input:not(:placeholder-shown) ~ .border::before,
.custom-field.three input.dirty ~ .border::before,
.custom-field.three input:focus ~ .border::after,
.custom-field.three input:not(:placeholder-shown) ~ .border::after,
.custom-field.three input.dirty ~ .border::after {
  width: 100%;
  height: 100%;
  border-width: var(--draw-line-width);
}

.custom-field.three input:not(:placeholder-shown) ~ .border::before,
.custom-field.three input.dirty ~ .border::before,
.custom-field.three input:focus ~ .border::before {
  transition-delay: 0s, var(--draw-duration), 0s;
}

.custom-field.three input:not(:placeholder-shown) ~ .border::after,
.custom-field.three input.dirty ~ .border::after,
.custom-field.three input:focus ~ .border::after {
  transition-delay: 
    calc(var(--draw-duration) * 2), 
    calc(var(--draw-duration) * 3), 
    calc(var(--draw-duration) * 2);
}
!

JS 

              
                /* Video Explanation - https://youtu.be/3AK3vspZvvM */
const inputs = document.querySelectorAll('input');

inputs.forEach(el => {
  el.addEventListener('blur', e => {
    if(e.target.value) {
      e.target.classList.add('dirty');
    } else {
      e.target.classList.remove('dirty');
    }
  })
})
!
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