.input {
    height: 52px;
    line-height: 52px;
    font-size: 32px;
    font-weight: bold;
 }

 .placeholder {
    font-size: 18px;
    font-weight: normal;
 }

<input class="input"
  value="{{ inputValue }}"
  type="digit"
  maxlength="12"
  placeholder="请输入xxx"
  placeholder-class="placeholder"
  focus
/>