Update Private Browsing theme to match new design

[brampitoyo]

Mockups

https://mozilla.invisionapp.com/share/9QRLVJI8UZK

Colour values

Primary Text	Second Text	Foundation	Above	Above dark	Accent	Accent Bright	Neutral
#FBFBFE (same as dark theme)	#A7A2B7 (same as dark theme)	linear-gradient(45deg, #7529A7 0%, #492E85 50%, #383372 100%);	#291D4F	Please generate this	#722291	#F565FF	#B1B1B3 (same as dark theme)

View these values alongside light and dark themes in the Color Audit document.

Private Browsing Mode settings doesn’t use its own theme. It follows the theme that has been set in the app.

CC @sblatz @mheubusch and @AmyYLee

┆Issue is synchronized with this Jira Task

[AmyYLee]

Updated link to spec https://mozilla.invisionapp.com/share/YFR8WRD8WJ9

[sblatz]

We're timeboxing this to a 3 so we don't spend too much time trying to get the toolbar looking correct with the gradient.

This does not include adding the trash can button back or the "delete session" button as we've decided to not move forward.

[sblatz]

Can I get some clarification on which of these colors I should be using for card highlights?

Also, the card highlight color should match the button colors used throughout (as it does in light and dark theme). So keep in mind this color will be used for those too!

cc: @AmyYLee

[AmyYLee]

@sblatz Hi! Can we update the highlight colour for PBM to be the same as the new Dark theme update for "Buttons"? Color: Violet 50 (#9059FF). Please see #1944 I think this simplifies things by having the same colour for buttons/toggles,switches/highlight tab colour for Dark theme and PBM.

[abodea]

Verified as fixed in the latest Nightly build from 7/24(190724(Build #12050609)) with Samsung Galaxy s10+(Android 9).

@sblatz can you please confirm that my verification is correct? I wanna make sure I understood correctly. The card that contain the URL should also be modified with this change?

[brampitoyo]

@sblatz @abodea Just noting the fact that the Private Browsing toolbar should also have a gradient, in addition to the homescreen background: https://mozilla.invisionapp.com/share/DST592EZKRP

Should this issue be reopened?

[abodea]

@brampitoyo I just verified with the latest Nightly build from 7/25 and the Private Browsing toolbar doesn't have a gradient, I will re-open this issue until it will be fixed.
Thank you!

[abodea]

Verified as fixed on the latest Nightly 7/31 with Samsung Galaxy s10+(Android 9).