实现修改el-table表格中的字体或背景颜色

需求：计算两数之差，并且在表格中显示，当差大于0，则当前的背景色或字体颜色为绿色，小于0则 显示其他颜色，等于0则正常显示

<el-table v-loading="loading" :data="list" highlight-current-row stripe border
 :header-cell-style="labelStyle" :cell-style="changeBg" height="580px">
    <el-table-column prop="country" width="100" align="center"></el-table-column>
    <el-table-column width="100" align="center">
        <template slot-scope="{ row }">
            {{ row.num1- row.num2}}
        </template>
    </el-table-column>
    <el-table-column prop="num1" label="数据1" min-width="100" align="center"></el-table-column>
    <el-table-column prop="num2" label="数据2" min-width="100"
                        align="center"></el-table-column>
</el-table>

/* data 部分 */
data() {
    return {
        labelStyle: {   //修改table 头部header样式
            fontSize: '24px',
            fontWeight: 600,
            color: '#585858',
        }
    }
}

/* methods 函数部分 */

// 改变table字体颜色
changeBg({ row, column, rowIndex, columnIndex }) {
            const diff = row.patsanp_patent_num - row.heima_patent_num;
            if (diff > 0 && columnIndex === 1) { // columnIndex 代表第几列
                return {
                    color: '#45A321',
                    fontWeight: 600
                }
            } else if (diff < 0 && columnIndex === 1) {
                return {
                    color: '#d11a32',
                    fontWeight: 600
                }
            } else if (diff == 0 && columnIndex === 1) {
                return {
                    color: '#000',
                }
            }
            else if (columnIndex === 0) {
                // 获取第二列的字体颜色
                const secondColumnColor = this.changeBg({
                    row,
                    column,
                    rowIndex,
                    columnIndex: 1
                }).color;
                return {
                    color: secondColumnColor,
                    fontWeight: 600
                };
            }
}