Menggunakan Purge CSS

Install:

npm i -D purgecss

Di package.json:

"scripts": {
    "purgecss": "purgecss --css public/dist/bootstrap.min.css --content src/**/*.svelte --output public/dist2",
    "build": "routify -b --dynamic-imports && rollup -c && npm run purgecss && node script/salin.js && node script/pakaiPurge.js",
},

Buat file public/dist2/.hello

Di .gitignore:

/public/dist2/bootstrap.min.css

Tambahkan di dist/global.css:

body{margin:0;font-family:-apple-system,BlinkMacSystemFont,"Segoe UI",Roboto,"Helvetica Neue",Arial,"Noto Sans",sans-serif,"Apple Color Emoji","Segoe UI Emoji","Segoe UI Symbol","Noto Color Emoji";font-size:1rem;font-weight:400;line-height:1.5;color:#212529;text-align:left;background-color:#fff}

Isi dari script/pakaiPurge.js:

fs = require('fs')
namaFile = 'hasil/index.html'
fs.readFile(namaFile, 'utf8', (_, x) => {
    x = x.replace('/dist/bootstrap.min.css', '/dist2/bootstrap.min.css')
    fs.writeFile(namaFile, x, 'utf8', () => {})
})

Hasil: https://svelte-brown.vercel.app/

Catatan: Dia kalau di Svelte kita pakai dynamic class (nggak ditulis langsung di htmlnya, nama classnya), purgecss nggak bisa deteksi. Solusinya pakai whitelist di option purgecss (ada di Google tutorialnya)