使用伪类

<div class="label-items">
  <p class="label">密码</p>
  <p class="label">用户名</p>
  <p class="label">身份证号</p>
</div>
​
.label-items {
	display: flex;
    flex-direction: row-reverse;
    width: 50%;
    margin-right: 20px;

    .label {
        width: 220px;
        text-align: justify;
    }

    .label::after {
        display: inline-block;
        width: 100%;
        content: '';
    }
}