Fix Gmail's Newest Annoyances with These Userstyles and Userscripts
Now that Gmail's rolled out its new look and you've learned your way around the changes, it's time to fix the little quirks and annoyances that remain. Here are a few of our favorite userstyles and userscripts for making the best of the Gmail redesign. 
These userscripts should work in Chrome, Firefox with Greasemonkey, or Safari withNinjakit. Chrome and Firefox users can install userstyles as userscripts from the individual styles' page or install them with Stylish for Chrome or Stylish for Firefox, which provides one-click userstyle installation. Opera users can install userstyles as plain CSS or JavaScript from the style's page.

Hide the "Send Feedback" Box

Fix Gmail's Newest Annoyances with These Userstyles and Userscripts
Certainly the most annoying thing about the new interface is its little "Send Feedback" box that always pops up in the bottom right-hand corner. Even if you click the X, it'll show back up again later on, taunting you and making you feel powerless. Thankfully, with this simple userscript, you can banish that box from Gmail forever.

Make Threads Easier to Read with Alternating Message Colors

Fix Gmail's Newest Annoyances with These Userstyles and Userscripts
In the new layout, it's a bit more difficult to tell the difference between two messages in a thread than it was in the old layout. They're both white, and have very thin borders. To more easily differentiate between messages in a conversation, you can install the Alternating Message Colorsuserstyle, which will color every other message light blue. You can choose to color the odd or even messages on the userstyle's page.

Increase the Contrast Between Read and Unread Messages

Fix Gmail's Newest Annoyances with These Userstyles and Userscripts
Google has also lightened a lot of the colors in this new design, meaning the difference between read and unread emails is a bit more difficult to see. If you'd like to darken the background of unread messages to more easily tell the difference, you can install theRead/Unread Contrast Increase userstyle. You can choose from two levels before installing: "A Little More" and "A Lot More", depending on how dark you want to make the background.

Differentiate Between Toolbar Buttons with Colors

Fix Gmail's Newest Annoyances with These Userstyles and Userscripts
One of my biggest gripes is that the buttons in Gmail's toolbar no longer have words on them, and the icons usually take a second to register since they're so light. The Easy Access Colored Buttons userstyle gives each button a different color, so you can instantly tell which is the delete button, which is the label button, and so on. Of course, if you don't like some of the colors, you can change them by fiddling with the style—I commented out a few lines with a /* because I thought certain buttons didn't look very good colored.

Make the Toolbar Even More Compact

Fix Gmail's Newest Annoyances with These Userstyles and Userscripts
If you're using the "Compact" version of Gmail's interface and still think it wastes too much space, you can install the Gmail Compact userscript for an even more efficient layout (especially useful for netbooks and other small screens). It makes the toolbar buttons a little smaller and moves the inbox a few pixels toward the left sidebar, as seen at the right.

Make the New Scrollbar Easier to See

Fix Gmail's Newest Annoyances with These Userstyles and Userscripts
Lastly, if you're using Chrome, you've probably noticed the new transparent scrollbars in Gmail. They can be tough to see on some themes, though, so if you'd like to make them a bit more visible, theVisible Scroll Bar userstyle will turn it a lovely shade of blue so it stands out a little more. And, if you're not on Chrome, you can get the cool Chrome-style scrollbar with the Scrollbar Like Chrome userstyle (though you won't be able to darken it with the first script, as it only works on Chrome).

Hopefully, a few of these will make your Gmail experience a little bit better. Of course, don't forget about all the other great Gmail userscripts we've featured in the past, including those contained in the awesome Better Gmail Firefox extension. Many of them still work with Gmail, even in the new layout. Got a favorite we didn't mention? Let us know about it in the comments.