I am not totally clear what you want, especially if it should be command line or GUI based.
You might be able to manage with a combination of the find and grep commands (pipe find output to grep).
That won’t take your tags into account.
Nor does my preferred solution : Double Commander.
Double Commander is my preferred Linux file manager, and if you ...
One solution could be to use Gulp + Critical extension.
It's a free cross platform CLI tool. And it allows to extract critical CSS and either embed it into HTML file or extract it to another CSS file.
When you get to configuring your gulpfile.js, here's mine which I've used while testing this:
const gulp = require('gulp');
const critical = ...
Written in C using GTK 3, part of the GNOME project
Source: Open source, see website or the Gitlab
License: GNU GPL v2
Supported audio formats: MP3, MP2, MP4/AAC, FLAC, Ogg Opus, Ogg Speex, Ogg Vorbis, MusePack, Monkey's Audio, and WavPack
Platforms: GNU/Linux, MS Windows
Having ImageMagick, potrace and pdftools (disclaimer: I am the author of pdftools). Assuming you have an input PDF file called input.pdf:
Convert every page in a BMP file using ImageMagick:
magick convert -density 300 input.pdf -quality 100 ./bmp/input.bmp
(optional) pre-process image files:
for /r %%i in (./bmp/*.bmp) do mkbitmap ...