输入框动画效果实现方法解析

.input-basic {
  padding: 10px;
  border: 2px solid #ccc;
  border-radius: 4px;
  outline: none;
  transition: border-color 0.3s ease;
}

.input-basic:focus {
  border-color: #007bff;
}

.input-underline {
  position: relative;
  border: none;
  padding: 10px 0;
  border-bottom: 2px solid #ddd;
  background: transparent;
  transition: border-bottom-color 0.3s;
}

.input-underline:focus {
  outline: none;
  border-bottom-color: transparent;
}

.input-underline:focus::after {
  content: '';
  position: absolute;
  left: 0;
  bottom: 0;
  width: 100%;
  height: 2px;
  background: #007bff;
  animation: extendLine 0.4s ease forwards;
}

@keyframes extendLine {
  from { width: 0; }
  to { width: 100%; }
}

.field {
  position: relative;
  margin: 20px 0;
}

.field input {
  padding: 10px;
  font-size: 16px;
  border: 1px solid #aaa;
  border-radius: 4px;
  outline: none;
  transition: all 0.3s;
}

.field label {
  position: absolute;
  left: 10px;
  top: 10px;
  font-size: 16px;
  color: #888;
  pointer-events: none;
  transition: 0.3s ease;
}

.field input:focus,
.field input:not(:placeholder-shown) {
  padding-top: 20px;
}

.field input:focus + label,
.field input:not(:placeholder-shown) + label {
  top: 2px;
  left: 8px;
  font-size: 12px;
  color: #007bff;
}

.input-shadow {
  padding: 10px;
  border: 1px solid #ccc;
  border-radius: 6px;
  outline: none;
  transition: box-shadow 0.3s;
}

.input-shadow:focus {
  box-shadow: 0 0 10px rgba(0, 123, 255, 0.3);
}