uni-data-menu sass报错

<style lang="scss">  
    .uni-menu-item {  
        display: flex;  
        align-items: center;  
        padding: 0 20px;  
        height: 56px;  
        line-height: 56px;  
        color: #303133;  
        transition: all 0.3s;  
        cursor: pointer;  
        // border-bottom: 1px #f5f5f5 solid;  
    }  

    .uni-menu-item:hover {  
        outline: none;  
        ***background-color: $sub-menu-bg-color;***  
        transition: all 0.3s;  
    }  

    .is-active {  
        color: #42B983;  
        // background-color: #ecf8f3;  
    }  

    .is-disabled {  
        // background-color: #f5f5f5;  
        color: #999;  
    }  

    .uni-menu-item.is-disabled:hover {  
        background-color: inherit;  
        color: #999;  
        cursor: not-allowed;  
    }  
</style>

在uni-data-menu插件中，有上面一段代码，其中 $sub-menu-bg-color 该颜色未定义，实际使用中报错