I found a solution, helped me this extantion GitHub - ecmel/vscode-html-css: Visual Studio Code Extension - CSS Intellisense for HTML · GitHub.
Thanks you so much Ecmel Ercan and @tme_317 for your thoughts!

But this extension not worked with HTML (EEx) files. I contributed to this. Until the author has merged pull-request, you can use my branch: https://github.com/reducio/vscode-html-css/tree/add-html-eex

git clone https://github.com/reducio/vscode-html-css/tree/add-html-eex
npm install
vsce package

# deps may be need, if you need hack this code
npm install -g typescript
npm install -g yo generator-code
npm install -g vsce
npm i -g @zeit/ncc

So, after run vsce package you get file vscode-html-css-0.2.3.vsix in root project folder.
Then you need install extension manually:

6613×510 50.3 KB

Don’t forget about settings of extension.
In settings.json add:

    "css.remoteStyleSheets": [
        "https://unpkg.com/tailwindcss@^1.0/dist/tailwind.min.css"
    ],

Usage:
You can view a list of attributes via ctrl + space.

Enjoy auto completion Tailwind CSS in your HTML (EEx) files.

Upvote, please: https://stackoverflow.com/questions/58013281/how-to-force-the-tailwind-css-intellisense-extension-for-vscode-work-with-html/58017659#58017659

This was changed again in elixir-ls 0.4.0

I changed my fork of vscode-tailwind to fix it:

You can try my solution:

1. Disable or uninstall original tailwindcss vscode extension
2. Download the latest *.vsix file Release v0.3.0 · praveenperera/vscode-tailwindcss · GitHub
3. Install the *.vsix file using command line ( Extension Marketplace )

ps: Thank to @praveenperera to provide the working extension