getComputedStyle(...) does NOT return pixel values in jsdom in Svelte - testing

Question

I am using jest and testing-library/svelte to write tests in SvelteKit. I have a simple text-component and want to test, if the line-height of the text is big enough depending on the font-size (because of accessibility reasons). For this, I want to use the window.getComputedStyle(...) method. However, if I am using it in a test, the font-size is NOT returned in pixel, but the unit I used in the actual css.
Text.svelte:
<div class="text">
<slot></slot>
</div>
<style>
.text {
text-align: left;
font-size: 1.2em;
line-height: 2.4em;
}
</style>
Text.spec.ts
/**
* #jest-environment jsdom
*/
import '#testing-library/jest-dom';
import { render } from "#testing-library/svelte";
import Text from "./Text.svelte";
describe("Text component", () => {
test("text must have a minimum line-height of 1.5x the font-size", () => {
const { container } = render(Text);
const textDiv = container.querySelector(".text");
const fontSize = window.getComputedStyle(textDiv).getPropertyValue('font-size')
const lineHeight = window.getComputedStyle(textDiv).getPropertyValue('line-height')
console.log("fontSize:", fontSize) // Output --> font-size: 1.2em
console.log("lineHeight:", lineHeight) // Output --> line-height: 2.4em
});
});
jest.config.cjs
module.exports = {
transform: {
"^.+\\.svelte$": [
"svelte-jester",
{ preprocess: "./svelte.config.js" },
],
"^.+\\.ts$": "ts-jest",
"^.+\\.js$": "ts-jest",
},
moduleFileExtensions: ["js", "ts", "svelte"],
moduleNameMapper: {
"^\\$lib(.*)$": "<rootDir>/src/lib$1",
"^\\$app(.*)$": [
"<rootDir>/.svelte-kit/dev/runtime/app$1",
"<rootDir>/.svelte-kit/build/runtime/app$1",
],
},
setupFilesAfterEnv: ["<rootDir>/jest-setup.ts"],
collectCoverageFrom: ["src/**/*.{ts,tsx,svelte,js,jsx}"],
};
jest-setup.ts
import "#testing-library/jest-dom";
Just in case, here are the relevant dependencies from my package.json
{
"devDependencies": {
"#testing-library/jest-dom": "^5.16.3",
"#testing-library/svelte": "^3.1.0",
"#types/jest": "^27.4.1",
"jest": "^27.5.1",
"svelte": "^3.46.6",
"svelte-check": "^2.2.6",
"svelte-jester": "^2.3.2",
"svelte-loader": "^3.1.2",
"svelte-preprocess": "^4.10.1",
"svelte2tsx": "^0.5.6",
"ts-jest": "^27.1.4",
"tslib": "^2.3.1",
"typescript": "~4.6.2"
},
"type": "module"
}
So how can I get the font-size and line-height in pixels. Is this even possible in a jest-test? I'd appreciate every answer, ideas or suggestions!