1、序言

        elementPlus、naive UI这些UI组件里面封装好了暗黑模式，直接使用相关api即可实现暗黑模式切换功能，而elementUI没有封装好，我们可以看看elementPlus、naive UI如何实现暗黑模式，然后在elementUI中模仿，从而实现暗黑模式！

2、vue3实现暗黑模式

        2.1、使用

（1）npm i @vueuse/core，  这个里面封装了很多hook工具函数：   VueUse | VueUse

（2）import { useDark, useToggle } from '@vueuse/core'

（3）在<script> 下使用：

<script setup>
import { useDark, useToggle} from '@vueuse/core'

const isDark = useDark();
</script>
<style scoped>

（4）useDark()可以获取当前的主题模式是不是暗黑模式，返回的是布尔值，useToggle()类似于开关，能将useDark()取反，实现主题模式切换效果

（5）main.js中引入暗黑模式的样式包：

 

        import 'element-plus/dist/index.css' ：引入elementplus推荐的light模式的样式文件

        import 'element-plus/theme-chalk/dark/css-vars.css'：是elementplus实现的dark模式的样式文件

 

        2.2、原理

        结论：暗黑模式时 import 'element-plus/theme-chalk/dark/css-vars.css'  覆盖 light模式中

import 'element-plus/dist/index.css' 的样式文件

        （1）会给html添加个class = "dark" 选择器

暗黑模式：

light模式

        （2）dark模式会在 'element-plus/theme-chalk/dark/css-vars.css'   进行样式覆盖

'element-plus/theme-chalk/dark/css-vars.css' 

html.dark {
    color-scheme: dark;
    --el-color-primary: #409eff;
    --el-color-primary-light-3: #3375b9;
    --el-color-primary-light-5: #2a598a;
    --el-color-primary-light-7: #213d5b;
    --el-color-primary-light-8: #1d3043;
    --el-color-primary-light-9: #18222c;
    --el-color-primary-dark-2: #66b1ff;
    --el-color-success: #67c23a;
    --el-color-success-light-3: #4e8e2f;
    --el-color-success-light-5: #3e6b27;
    --el-color-success-light-7: #2d481f;
    --el-color-success-light-8: #25371c;
    --el-color-success-light-9: #1c2518;
    --el-color-success-dark-2: #85ce61;
    --el-color-warning: #e6a23c;
    --el-color-warning-light-3: #a77730;
    --el-color-warning-light-5: #7d5b28;
    --el-color-warning-light-7: #533f20;
    --el-color-warning-light-8: #3e301c;
    --el-color-warning-light-9: #292218;
    --el-color-warning-dark-2: #ebb563;
    --el-color-danger: #f56c6c;
    --el-color-danger-light-3: #b25252;
    --el-color-danger-light-5: #854040;
    --el-color-danger-light-7: #582e2e;
    --el-color-danger-light-8: #412626;
    --el-color-danger-light-9: #2b1d1d;
    --el-color-danger-dark-2: #f78989;
    --el-color-error: #f56c6c;
    --el-color-error-light-3: #b25252;
    --el-color-error-light-5: #854040;
    --el-color-error-light-7: #582e2e;
    --el-color-error-light-8: #412626;
    --el-color-error-light-9: #2b1d1d;
    --el-color-error-dark-2: #f78989;
    --el-color-info: #909399;
    --el-color-info-light-3: #6b6d71;
    --el-color-info-light-5: #525457;
    --el-color-info-light-7: #393a3c;
    --el-color-info-light-8: #2d2d2f;
    --el-color-info-light-9: #202121;
    --el-color-info-dark-2: #a6a9ad;
    --el-box-shadow: 0px 12px 32px 4px rgba(0, 0, 0, 0.36), 0px 8px 20px rgba(0, 0, 0, 0.72);
    --el-box-shadow-light: 0px 0px 12px rgba(0, 0, 0, 0.72);
    --el-box-shadow-lighter: 0px 0px 6px rgba(0, 0, 0, 0.72);
    --el-box-shadow-dark: 0px 16px 48px 16px rgba(0, 0, 0, 0.72), 0px 12px 32px #000000, 0px 8px 16px -8px #000000;
    --el-bg-color-page: #0a0a0a;
    --el-bg-color: #141414;
    --el-bg-color-overlay: #1d1e1f;
    --el-text-color-primary: #E5EAF3;
    --el-text-color-regular: #CFD3DC;
    --el-text-color-secondary: #A3A6AD;
    --el-text-color-placeholder: #8D9095;
    --el-text-color-disabled: #6C6E72;
    --el-border-color-darker: #636466;
    --el-border-color-dark: #58585B;
    --el-border-color: #4C4D4F;
    --el-border-color-light: #414243;
    --el-border-color-lighter: #363637;
    --el-border-color-extra-light: #2B2B2C;
    --el-fill-color-darker: #424243;
    --el-fill-color-dark: #39393A;
    --el-fill-color: #303030;
    --el-fill-color-light: #262727;
    --el-fill-color-lighter: #1D1D1D;
    --el-fill-color-extra-light: #191919;
    --el-fill-color-blank: transparent;
    --el-mask-color: rgba(0, 0, 0, 0.8);
    --el-mask-color-extra-light: rgba(0, 0, 0, 0.3)
}

html.dark .el-button {
    --el-button-disabled-text-color: rgba(255, 255, 255, 0.5)
}

html.dark .el-card {
    --el-card-bg-color: var(--el-bg-color-overlay)
}

html.dark .el-empty {
    --el-empty-fill-color-0: var(--el-color-black);
    --el-empty-fill-color-1: #4b4b52;
    --el-empty-fill-color-2: #36383d;
    --el-empty-fill-color-3: #1e1e20;
    --el-empty-fill-color-4: #262629;
    --el-empty-fill-color-5: #202124;
    --el-empty-fill-color-6: #212224;
    --el-empty-fill-color-7: #1b1c1f;
    --el-empty-fill-color-8: #1c1d1f;
    --el-empty-fill-color-9: #18181a
}

        （3）css文件中，--开头的为自定义变量，要使用它时var(--自定义变量)，从而实现变量复用，减少冗余的css样式

        （4）举个例子：el-card

element-plus/dist/index.css 文件中

  'element-plus/theme-chalk/dark/css-vars.css' 文件中 

3、vue2实现暗黑模式

        3.1、实现

        （1）建立一个暗黑主题样式文件：my-theme.css，并将其引入到main.js中

        （2）my-theme.css文件中 自己根据chrome浏览器的样式工具进行调整了，html.dark为父选择器

 示范：在my-theme.css 中根据需求调节出自己想要的样式

html.dark .el-submenu__title {
    background-color: #121212;
    color: #fff;
}

html.dark .el-submenu__title:hover {
    background-color: #18222b;
}

html.dark .el-menu--inline {
    background-color: #121212;
    color: #fff;
}

html.dark .el-menu-item.is-active {
    color: var(--el-color-primary);
}

html.dark .el-menu-item {
    background-color: #121212;
    color: #fff;
}

html.dark .el-menu-item:hover {
    background-color: #18222b;
}


html.dark .el-card {
    background-color: #121212;
}

        （3）添加一个开关用于给html添加class="dark"选择器，也就是暗黑模式

<template>
    <el-switch v-model="isDark" @change="changeMode" active-color="#13ce66" inactive-color="#ff4949">
    </el-switch>
</template>

<script>
export default {
    data() {
        return {
            isDark: false,
        }
    },
    methods: {
        // 模式切换
        changeMode(val) {
            // 获取html根元素标签
            let html = document.documentElement
            if (val) {
                // html添加class="dark"选择器
                html.classList.add('dark')
            } else {
                // html移除class="dark"选择器
                html.classList.remove('dark')
            }
        }
    }
}
</script>