If you are a git user, you can install the theme by cloning the repo:
$ git clone https://github.com/getomni/Vivaldi.git
Download using the GitHub .zip download option and unzip them.
- Open Vivaldi's Settings panel
- On Windows: Vivaldi menu > Tools > Settings
- On Linux: Tools menu > Settings
- On macOS: Vivaldi menu > Preferences
- Select Themes in the sidebar
- Click the + sign, enter a name (ex: omni)
- Enter the following colors from the file Colors.