标签和输入框要在一行

可以将 `el-form-item` 的样式设置为 `display: flex; justify-content: space-between; align-items: center;`，同时将 `label` 标签的宽度设置为固定值，如 `width: 100px;`。这样，每个表单项的标签和输入框就会在同一行，并且标签的宽度也会固定。完整代码如下：

<div style="display: flex; justify-content: center; align-items: center; width: 700px; margin: 0 auto;">
  <el-form :model="user" status-icon :rules="rules" ref="ruleForm" class="demo-ruleForm" style="width: 100%;">
    <el-form-item label="密码" prop="username" style="display: flex; justify-content: space-between; align-items: center; width: 100%;">
      <span style="width: 100px;">密码：</span>
      <el-input type="password" v-model="user.pass" autocomplete="off" width="250px"></el-input>
    </el-form-item>
    <el-form-item label="确认密码" prop="password" style="display: flex; justify-content: space-between; align-items: center; width: 100%;">
      <span style="width: 100px;">确认密码：</span>
      <el-input type="password" v-model="user.checkPass" autocomplete="off"></el-input>
    </el-form-item>
    <el-form-item label="身份" prop="rank" style="display: flex; justify-content: space-between; align-items: center; width: 100%;">
      <span style="width: 100px;">身份：</span>
      <el-select v-model="user.rank" placeholder="请选择">
        <el-option v-for="item in options" :key="item.value" :label="item.label" :value="item.value">
        </el-option>
      </el-select>
    </el-form-item>
    <el-form-item style="display: flex; justify-content: center; align-items: center; width: 100%;">
      <el-button type="primary" @click="submitForm">提交</el-button>
      <el-button @click="resetForm">重置</el-button>
    </el-form-item>
  </el-form>
</div>