How save text, svg, html, css all together efficiently
i dont known if it helps but, Opera browser offer an option to save the webpages to an unique file { mht extension }, this stores all the files { css, images, scripts, etc } in base64 encoded text for a later use { when the document is opened }... maybe this can be a way to store data :P
I manage a webapp where users generate reports, and found it more efficient to store images and binary files in the filesystem, and link to them from the database. Elements that are in xml or text are kept in the database for easier searching - in your case this would include css/html and svg (which is xml). Use the database for managing revisions.
Might also check out this thread on storing images in a database.
It looks like Frabic.js is using the node.js javascript webserver on the backend - haven't used this before, but you might investigate which databases are easiest to use with node.js:
If you want to query the text efficiently, then perhaps putting all bits of information into the DB separately is the most efficient. Maybe you with to play with OOXML or ODF, that may serve as container for all information you require, and then XML-storage (e.g. eXist) to store it and query (e.g. the text). As these standards are XML-based, you can transform them into HTML (e.g. here or here) but writing an online editor for this is something that monster like Google can do.