headless and not headless mode are rendering the same page in a little different mode

Steps to reproduce

Tell us about your environment:

C:\src\jest-image-snapshot-example>npm list --depth=0
jest-image-snapshot-example@1.0.0 C:\src\jest-image-snapshot-example
+-- jest@24.9.0
+-- jest-image-snapshot@2.11.1
`-- puppeteer@2.0.0

C:\src\jest-image-snapshot-example>node --version
v12.13.0

Windows 10 64 bit updated.

What steps will reproduce the problem?

1. clone this repository https://github.com/andreabisello/jest-image-snapshot-example and runs “headless-differences.test.js”. OR
2. run this test, got the screenshot
3. activate headless mode, got the screenshot.

const puppeteer = require('puppeteer')
const { toMatchImageSnapshot } = require('jest-image-snapshot');
expect.extend({ toMatchImageSnapshot });

describe('headless differences Test', () => {

    test("headless and not headless screenshot should to be the same", async () => {
        jest.setTimeout(15000)
        browser = await puppeteer.launch({
            headless: false,
            defaultViewport: {width: 1800, height: 900},
            args: ["--start-maximized"],
            devtools: false
        })
        page = await browser.newPage()
        await page.goto("https://legaltest.solutiondocondemand.com", {
            timeout: 20000,
            waitUntil: ['load', 'domcontentloaded', 'networkidle0', 'networkidle2']
        })
        loginBox = await page.waitForSelector('#loginBox', {visible: true, timeout:30000})

        //removing time variant area
        await page.evaluate(() => {
            document.querySelector('#lblNow').style.visibility = "hidden"
        })

        //taking screenshot
        const loginBoxScreenshot = await loginBox.screenshot()
        expect(loginBoxScreenshot).toMatchImageSnapshot({
            failureThreshold: 0,
            failureThresholdType: "percent"
        })
        await browser.close()
    })
})

What is the expected result?

this test will open a url and take a screenshot of the login form. There should be no differences in the login form in headless or not headless mode.

What happens instead?

even i removed the time variant part of the page ( the one with the data ) , screenshot are ~1% different.

Differences are

1. fonts rendering.
2. Login button have a kind of yellow border

[saratrionfetti]

I also have differences between same screenshots when I change the headless property. This is my case:

[OrKoN]

Screenshots are already platform dependent (e.g., you would get slight differences on Mac vs Windows vs Linux) and different modes are not supposed to be identical. Also, please try using the new headless mode (headless: chrome) that is meant to be the same browser implementation as the headful mode. The old headless mode is actually a different browser underneath.