When developing the project with Svelte, I encountered the need to convert PX into REM. I tried postCSS plug-ins such as PostCSS-Px2REM and PostCSS-PxtoREM, but failed. Finally, I found the plug-ins of PostCSS-Units and succeeded in implementing them. The complete rollup configuration files are as follows: 3.3.2 Case to REM The configuration is sapper project configuration

import path from 'path';
import resolve from '@rollup/plugin-node-resolve';
import replace from '@rollup/plugin-replace';
import commonjs from '@rollup/plugin-commonjs';
import url from '@rollup/plugin-url';
import svelte from 'rollup-plugin-svelte';
import babel from '@rollup/plugin-babel';
import { terser } from 'rollup-plugin-terser';
import config from 'sapper/config/rollup.js';
import pkg from './package.json';
import sveltePreprocess from 'svelte-preprocess';
// import { less } from 'svelte-preprocess';
const postcssUnits = require('postcss-units');

const mode = process.env.NODE_ENV;
const dev = mode === 'development';
constlegacy = !! process.env.SAPPER_LEGACY_BUILD;const onwarn = (warning, onwarn) = >
	(warning.code === 'MISSING_EXPORT' && /'preload'/.test(warning.message)) ||
	(warning.code === 'CIRCULAR_DEPENDENCY' && /[/\\]@sapper[/\\]/.test(warning.message)) ||
	onwarn(warning);

export default {
	client: {
		input: config.client.input(),
		output: config.client.output(),
		plugins: [
			replace({
				'process.browser': true.'process.env.NODE_ENV': JSON.stringify(mode)
			}),
			svelte({
				dev,
				hydratable: true.emitCss: true.// preprocess: [
				// less(),
				// ]
				preprocess: sveltePreprocess({
					postcss: {
						plugins: [
							postcssUnits({
								size: 75
							}),
						]
					},
				}),
			}),
			url({
				sourceDir: path.resolve(__dirname, 'src/node_modules/images'),
				publicPath: '/client/'
			}),
			resolve({
				browser: true.dedupe: ['svelte']
			}),
			commonjs(),

			legacy && babel({
				extensions: ['.js'.'.mjs'.'.html'.'.svelte'].babelHelpers: 'runtime'.exclude: ['node_modules/@babel/**'].presets: [['@babel/preset-env', {
						targets: '> 0.25%, not dead'}]],plugins: [
					'@babel/plugin-syntax-dynamic-import'['@babel/plugin-transform-runtime', {
						useESModules: true}}]]),! dev && terser({module: true}),].preserveEntrySignatures: false,
		onwarn,
	},

	server: {
		input: config.server.input(),
		output: config.server.output(),
		plugins: [
			replace({
				'process.browser': false.'process.env.NODE_ENV': JSON.stringify(mode)
			}),
			svelte({
				generate: 'ssr'.hydratable: true,
				dev,
				// preprocess: [
				// less(),
				// ]
				preprocess: sveltePreprocess({
					postcss: {
						plugins: [
							postcssUnits({
								size: 75
							}),
						]
					},
				}),
			}),
			url({
				sourceDir: path.resolve(__dirname, 'src/node_modules/images'),
				publicPath: '/client/'.emitFiles: false // already emitted by client build
			}),
			resolve({
				dedupe: ['svelte']
			}),
			commonjs(),
		],
		external: Object.keys(pkg.dependencies).concat(require('module').builtinModules),

		preserveEntrySignatures: 'strict',
		onwarn,
	},

	serviceworker: {
		input: config.serviceworker.input(),
		output: config.serviceworker.output(),
		plugins: [
			resolve(),
			replace({
				'process.browser': true.'process.env.NODE_ENV': JSON.stringify(mode) }), commonjs(), ! dev && terser() ],preserveEntrySignatures: false,
		onwarn,
	}
};
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After the configuration, modify the CSS as follows:

h2 {
	font-size: rem(42);
	line-height: rem(60);
	text-align: center;
}
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Original: www.yuedun.wang/blogdetail/…