I have been trying to do this for a while now but feels like I'm having more trouble than what I should so I decided to ask. I want to use display an HTML file from my computer in the node red dashboard. I also want to be able to edit the format of this using CSS. Once I can do this I will like to get MQTT messages and display them on the "website".
The only way to do that is to use an
<iframe> tag. Or to deconstruct the HMTL and include it in a ui_template file.
Both of the above will let you do that.
You will then be better off putting the design into a ui_tempate.
However, if you really don't need the other features of the Dashboard, you would most likely be better off using uibuilder. This will provide the websocket comms support for you and you can use your own html file directly simply by putting it in the right folder.
While uibuilder comes with VueJS, you don't have to use it. All you need is the uibuilderfe library.