Well you could do that for a long time with MHTML, WARC, etc. downloaders, including those available in browsers via "Save Page as", though CSS imports aren't covered by older tools (are they by yours?). Anyway, congrats for completing this as a Rust first-timer project, which certainly speaks to the quality of the Rust ecosystem. For using this approach as offline browser, of course, the problem is that Ajax-heavy pages using Javascript for loading content won't work, including every React and Vue sites created in the last five years (but you could make the point those aren't worth your attention as a reader anyway).