Minor UI updates to the in-app tour

[amandacilek-zz]

Relates to #5679, #5680, #5681, #5682. Full design spec: https://docs.google.com/document/d/1ErZ7eC-Cbrsgwu0uaIfGq9ZeLuhma1h5K0xvYeRv2KU/edit#

We would like to make some updates to the in-app tour experience starting with v 3.8. The updates include some minor UI improvements (this ticket) as well as a new updated script and updated table of contents page (separate ticket).

• Ensure that the font is Noto Sans (currently displays as Helvetica in my browser)
• The title text should be 16px bold. The body text can remain 14px for now but we should consider making this match our standard 16px at some point.
• Remove the grey background from the title area and instead add a 1px grey line separating the title from the main text content. This line should be 40px from the top of the window.
• There should be a 20px gap between the left edge of the text and the left edge of the pop-up window. This 20px buffer is also true for the buttons.
• Remove the “End tour” text link and instead add a normal “x” to close icon in the upper right corner
• Keep the "Previous" button in the lower left corner, but move the "Next" button to the far right corner
• Style the "Next" button like our standard active blue buttons

[michaelkohn]

Until we implement #5681 (linking tours), I think this issue will still need to address what the buttons should look like for the first and last steps of a tour. Below I've included what it looks like today (in v3.7.0) for forms, and how I would suggest we handle it for Guided Tour steps until we start linking tours.

Here is how it works for forms

Form page	Bottom Left Button	Bottom Right Button
First	Not shown	Blue "Next »"
Middle	White "≪ Prev"	Blue "Next »"
Last	White "≪ Prev"	Blue "Submit"

Here is how I suggest we do it for the Guided Tour

Tour step	Bottom Left Button	Bottom Right Button
First	Don't show	Blue "Next »"
Middle	White "≪ Prev"	Blue "Next »"
Last	White "≪ Prev"	Blue "Finish"

NOTE: If a button is shown, it should be active.

[ngaruko]

Guided tour removed.