There's no need to base64 encode HTML, since it's already plaintext. You can just omit the encoding declaration in the data URL and include the raw HTML, e.g.

There's no need to base64 encode HTML, since it's already plaintext. You can just omit the encoding declaration in the data URL and include the raw HTML, e.g. 'data:text/html,<html><body><h1>Hello, world!</h1></body></html>'. That should save a bit of overhead.