el-table多选表头复选框不对齐

 <el-table
            ref="multipleTable"
            :data="DataList"
            tooltip-effect="dark"
            style="width: 100%"
            height="250"
            @selection-change="handleSelectionChange">
          <el-table-column
              type="selection"
              width="55" >
          </el-table-column>
          <el-table-column
              prop="jskMingcheng"
              label="姓名"
              width="120">
          </el-table-column>
          <el-table-column
              prop="jskDanwei"
              label="单位"
              show-overflow-tooltip>
          </el-table-column>
        </el-table>

   <el-table-column
              type="selection"
              width="55" 
              align="center">
          </el-table-column>