Why does code always look better in Gitlab/GitHub than in my editor?

No matter how much I fine-tune my editor (these days I only use VSCode), code always feels more pleasant and polished when I see it in GitLab or GitHub compared to inside the editor itself.

I've tried different themes, fonts, colours, even tried to mimic the same look as the web UI (after all, VSCode is also Electron-based!), but I still get the same impression: code looks cleaner and somehow more readable in the browser.

Has anyone else experienced this?