Ouch 
. Sorry that I haven’t been as responsive as I usually am this week, I’ve been on travel.
Also, the docs are here: GitHub - plotly/dash-docs: 📖 ISSUE TRACKER ONLY for The Official Dash Userguide & Documentation https://dash.plotly.com/. Feel free to open an issue or a PR for a particular topic that should be explored.
There are many questions about this that have already been asked and answered on the forum:
- Search bootstrap: Search results for 'bootstrap category:16' - Plotly Community Forum
- Search raw html: Search results for 'raw html category:16' - Plotly Community Forum
- Search local css: https://community.plotly.com/search?q=local%20css%20category%3A16
In particular, these issues might help you out here. It’s not clear from your question if you are trying to use the HTML directly (not recommended, translate it to dash_html_components) or if you are just wondering how to use local css.
- Local CSS: How do I use Dash to add local css? - #27 by nicolaskruchten
- General discussion about Bootstrap: Getting Bootstrap components working is currently clunky with python API - #2 by chriddyp
- Raw HTML vs Dash Components: Flexibility and compatibility with html templating inside Dash layout - #2 by chriddyp
Also, it’d be helpful if you could share a small, reproducable example that shows what you have tried so far, and then other folks can help you take it the last mile. It looks like you figured it out though!