Sublime Text is great, but it's sidebar doesn't match the default (and beautiful) dark Monokai theme. Thanks to this gist and after tweaking it a little (I corrected a glitch with the code collapse icon and made the higlight color lighter), I finally made it look great:

To install, put "Default.sublime-theme" file in "[SUBLIME]/packages/Theme/". (extra "Theme' directory is not necessary for it to function but it keeps the file structure a little neater imo.)

Installation via Terminal

macOS:

cd sublime-monokai-sidebar/

mkdir /Users/$USER/Library/Application\ Support/Sublime\ Text\ 3/Packages/Theme 

mv Default.sublime-theme /Users/$USER/Library/Application\ Support/Sublime\ Text\ 3/Packages/Theme/

Linux:

cd sublime-monokai-sidebar/

mkdir /home/$USER/.config/sublime-text-3/Packages/Theme

mv Default.sublime-theme /home/$USER/.config/sublime-text-3/Packages/Theme

Installation using other methods:

Windows (File Explorer):
     copy file to user directory here:
       %userprofile%\AppData\Roaming\Sublime Text 3\Packages\User\Theme

Using Sublime Text 3:
       type ctl + shift + p or shift + cmd + p to open Command Palette.
     type:
       Preferences: Browse Packages; then hit enter to select
       Create directory i.e. "Theme" then place the file Default.sublime-theme in your new directory