通过 CSS 变量设置主题色，几乎所有浏览器都支持CSS变量。可以动态地改变组件内的个别变量，以便更好地自定义组件样式，而不需要修改 SCSS 文件重新编译一次。

1.首先增加工具类 theme.js

// 处理主题样式
export function handleThemeStyle(theme) {
	document.documentElement.style.setProperty('--el-color-primary', theme)
	for (let i = 1; i <= 9; i++) {
		document.documentElement.style.setProperty(`--el-color-primary-light-${i}`, `${getLightColor(theme, i / 10)}`)
	}
	for (let i = 1; i <= 9; i++) {
		document.documentElement.style.setProperty(`--el-color-primary-dark-${i}`, `${getDarkColor(theme, i / 10)}`)
	}
}

// hex颜色转rgb颜色
export function hexToRgb(str) {
	str = str.replace('#', '')
	let hexs = str.match(/../g)
	for (let i = 0; i < 3; i++) {
		hexs[i] = parseInt(hexs[i], 16)
	}
	return hexs
}

// rgb颜色转Hex颜色
export function rgbToHex(r, g, b) {
	let hexs = [r.toString(16), g.toString(16), b.toString(16)]
	for (let i = 0; i < 3; i++) {
		if (hexs[i].length == 1) {
			hexs[i] = `0${hexs[i]}`
		}
	}
	return `#${hexs.join('')}`
}

// 变浅颜色值
export function getLightColor(color, level) {
	let rgb = hexToRgb(color)
	for (let i = 0; i < 3; i++) {
		rgb[i] = Math.floor((255 - rgb[i]) * level + rgb[i])
	}
	return rgbToHex(rgb[0], rgb[1], rgb[2])
}

// 变深颜色值
export function getDarkColor(color, level) {
	let rgb = hexToRgb(color)
	for (let i = 0; i < 3; i++) {
		rgb[i] = Math.floor(rgb[i] * (1 - level))
	}
	return rgbToHex(rgb[0], rgb[1], rgb[2])
}

2.在App.vue中初始化加载主题样式

<script setup>
import {onMounted, nextTick} from 'vue'
import { handleThemeStyle } from '@/utils/theme'

onMounted(() => {
  nextTick(() => {
    // 初始化主题样式
    handleThemeStyle('#409EFF')
  })
})
</script>