restyle 404

[jdamiba]

closes plotly/documentation#1678

[nicolaskruchten]

Style looks good. Now time to make the content more helpful! Let's get a search box in there somehow if there is /python/ or /javascript/ or /r/ in the URL so they can search our docs directly? Maybe use Javascript to preload the search box with the URL subfragment with hyphens replaced by spaces, along with a "search" button they can click on that will bring up the modal? So like for the URL https://plotly.com/python/datashaader/ (note the extra a) we know they're in Python-land, and maybe searching for datashaader will come up with something? and yes, our search will get them to where they're going!

[jdamiba]

• get search modal to display on 404 page (change layout to base?)
• prepopulate search modal with URL
• if URL contains /python, /javascript, or /r, then provide a link to language index page

[jdamiba]

@nicolaskruchten I'd like to suggest that we merge this style update on its own.

Adding the search modal to this page is more complicated than I had anticipated and I don't want that work to block this update, which looks more on brand than what we currently have in production.

[nicolaskruchten]

OK, in that case please:

• put a bit of whitespace above the header
• Change the text to "404 - Page not found!"
• Add a link below it: Back to Graphing Libraries documentation home

[jdamiba]

@nicolaskruchten I have updated this PR.

Screenshot:

[nicolaskruchten]

Can we make the link look more like a link? change color, make it underlined?

[jdamiba]