Best combined with:
FT DeepDark add-on by steva (Stefano Roselli) (Firefox Only)

DeepDark Theme by actualmanx (Chrome only) https://chrome.google.com/webstore/detail/deep-dark/eeffcpnmcmfdfnaadpnkldhkcjjiihcf

DeepDark Scroll Bars extension by actualmanx (Chrome only) https://chrome.google.com/webstore/detail/deep-dark-scrollbars/feeaojjpfjaggengmoigjlckepbmkane

Dark Fusion - Google by DeathTBO - http://freestyler.ws/style/118354/dark-fusion-google

03/20/2017 - Added option to remove the "TRY NOW" banner for linking to the new google voice.
02/13/2017 - Removed hangouts opt-in notice option. No longer shows up after latest google voice update.
08/24/2016 - Added option to hide the hangouts opt-in notice message. Inverted help icons and sidebar icons.
11/06/2015 - Removed google bar theming. Now uses Google Bar - Dark Style theme for bar elements.
06/19/2015 - Updated description. Older chrome theme now obsolete.
11/30/2014 - Updated screenshot.
09/18/2014 - Styled Hangouts integration popup and reminder banner about hangouts integration.
09/16/2014 - Google bar color div name update. I will try to continue to keep this updated even though hangouts is the new place for Google Voice texting unless you opt out. Looks like the hangouts related updates to this page are being themed fairly well so I will leave them as is.
09/08/2014 - Google bar color div name update.
09/01/2014 - Fixed text color for voicemail "no translation available" text. Fixed voicemail play button hover issue. Still not perfect but almost 100%.
08/08/2014 - Google bar color div name update.
07/29/2014 - Removed image replacements for google bar because it's just too damn annoying to update. Updated div name and switched to gray top bar so images don't need to be replaced. I left the image replacement code in tact in case you want to still play with the offsets (cough cough Devo cough cough).
07/28/2014 - Removed reliance on GT Deepdark style for google bar. Sr21 no longer updating it and thus a fix was needed. New maintainer changed some things that cause buttons and images to not theme properly with my setup. Thanks to Devo for his donated code to theme the google bar. It's simpler but also more resistant to google changes as a result. If you want to keep using FT Deepdark then make sure that google voice domain is not themed. I will request it to not be included by default. Otherwise the whole page will be messed up. Change the matching url regexp to this: "(https|http)://(www|encrypted|images|translate)\.google\.(com|([a-z]{2}))(\.[a-z]{2})?/(?!mobile|intl|alerts|shopping|finance|calendar|nexus|contacts|webmasters|services|advanced_search|voice).*"
Also fixed refresh button and voicemail playback buttons which had been previously working with old GT Deepdark.
06/13/2014 - Transcript buttons and the rest of the settings page buttons now themed.
06/10/2014 - Set default contact photo to darker inverted version of image.
05/27/2014 - Set split pane handle (vertical separator) explicitly hidden. Popped up as visible for some reason.
04/22/2014 - Background color lightened just a bit. Thanks Devo for the suggestion.
03/25/2014 - Fix phones list tab in settings page.
03/22/2014 - Fixed some minor copy/paste issues where line feeds got thrown in.
03/21/2014 - Since the google bar has changed significantly and was now integrated into google voice, instead of re-inventing the wheel I decided to simply combine this with the GT DeepDark for Google style by Sr21 (http://freestyler.ws/style/76580/gt-deepdark-for-google). First download and enable that style, or else the google bar will remain white/unstyled. I did an overhaul of my style to match the DeepDark style better, mainly lightened up the blue text and highlights to match the slushie blue color, and also fixed any conflicting styled elements. I want to credit Sr21 for the nice button styling which I grabbed for this. Also, the themed html5 voice player seems to work in firefox now and no longer uses the flash based player. Tested with latest versions of Google Chrome and Firefox
02/25/2013 - The little question mark image for the help link next to the google contacts link on the sidebar is now transparent. Still clickable but the unsightly white image is now gone.
01/06/2013 - Voicemail playback interface now themed. This will work only for Google Chrome users because Firefox uses a flash-based player which cannot be themed.
09/22/2012 - Updated voicemail play button url reference to be absolute rather than relative to conform to userstyles newly added guidelines for image linking. This should not affect the site style at all.

Initial release - Let's call this v0.1. I based this off of neyel8r's Google Voice - Dark & Blue theme (http://freestyler.ws/style/49764/google-voice-dark). I also used code from Kemwer's Google Reader - Kemwer Black (http://freestyler.ws/style/49154/google-reader-kemwer-black) and stormi's Perfect Dark Google Maps (http://freestyler.ws/style/34580/perfect-dark-google-maps)

This was tested in latest version of Chrome and Firefox. It looks best in chrome mainly due to voicemail buttons, but pretty much identical. Some of the code may be a duplicate functionality or even not do anything at all. I just tweaked it until it all worked.