UserAgent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/65.0.3325.181 Safari/537.36

Steps to reproduce the problem:
1. I use puppeteer @1.3.0 and chrome @68.0.3398.0
2. Generate PDF 

const puppeteer = require('puppeteer');

(async () => {
    const browser = await puppeteer.launch();
    const page = await browser.newPage();

    const content = '<h1 style="font-size:20px;margin: 0;">First <span style="background: yellow">second</span> third</h1>'; 

    try {
        await page.setContent(content);
        await page.pdf({
            displayHeaderFooter: true,
            path: 'size_bug.pdf',
            printBackground: true,
            headerTemplate: content,
            margin: {
              top: '60px'
            }
        });
    } catch (e) {
        console.error(`Something went wrong: ${e.message}`);
    } finally {
        await browser.close();
    }
})();

What is the expected behavior?
Font size should be the same in header and in main content.

What went wrong?
The font size is 20 in header and 15 in main content in spite of html font-size:'20px'

Did this work before? No 

Chrome version: 68.0.3398.0  Channel: dev
OS Version: 10.0
Flash Version:
 

Deleted: size_bug.pdf 77.9 KB

size_bug.pdf 77.9 KB Download

Deleted: 2018-04-14_1427.png 22.5 KB

	2018-04-14_1427.png 22.5 KB View Download