“Note that, of the three layers above, only the UI layer is closed-source. Roughly 92% of the browser’s code is open source coming from Chromium, 3% is open source coming from us, which leaves only 5% for our UI closed-source code.”
Straight from the horses mouth. So 92% of it is the same as every other chromium browser. 3% is their oss code and 5% is closed source. That 5% more than actual open source browsers.