CSS实现placeholder动画效果详解

input::placeholder {
  color: #999;
  font-style: italic;
  transition: all 0.3s ease;
}

input::-webkit-input-placeholder { color: #999; }
input::-moz-placeholder          { color: #999; }
input:-ms-input-placeholder     { color: #999; }

<div class="input-group">
  &lt;input type=&quot;text&quot; id=&quot;name&quot; required&gt;
  <label for="name">姓名</label>
</div>

.input-group {
  position: relative;
  margin: 20px 0;
}

input {
  width: 100%;
  padding: 10px;
  border: 1px solid #ccc;
  border-radius: 4px;
  outline: none;
}

label {
  position: absolute;
  left: 10px;
  top: 10px;
  color: #999;
  font-size: 16px;
  pointer-events: none;
  transition: 0.3s ease all;
}

input:focus ~ label,
input:valid ~ label {
  top: -10px;
  left: 5px;
  font-size: 12px;
  color: #007bff;
  background: white;
  padding: 0 4px;
}

input.fade-placeholder::placeholder {
  opacity: 0;
  transition: opacity 0.3s ease;
}

const input = document.getElementById('name');
input.addEventListener('focus', () => {
  input.classList.add('fade-placeholder');
});
input.addEventListener('blur', () => {
  if (!input.value) {
    input.classList.remove('fade-placeholder');
  }
});