When Google Chrome first came out for Windows, people were hacking .dll files to change the theme. Now, with theme support, many still find they can’t reliably switch between installed themes, but have to install them again from the download page. This is certainly true of the Linux version (at least in Ubuntu), as the Extensions page tells you none are installed.
I’ve seen talk from Windows users of finding all the installed themes in an extensions folder, but currently in the Linux version you will not only find that there is no .crx file (the extension of the themes) belonging to this program to be found anywhere, but no file at all with the name/prefix of the installed theme.
When you choose to install a theme, it gets downloaded as usual, but then disappears from your ~/Downloads folder once it is installed.
So the way around this is not to click any Install buttons, but to right-click them and choose “Save Link As“. Then just save each desired theme where you can easily find them all, like a new folder called ~/Downloads/Google Chrome Themes. Note that if you’re at a gallery page with previews of lots of themes, you’ll need to go to each theme’s page and right-click the Install button there (otherwise you’ll be downloading .html web pages, not a .crx themes).
Once you’ve downloaded some, all you need to do is drag one and drop it anywhere on Google Chrome. You will see a confirmation appear at the bottom left, so click the Continue button to proceed with changing the theme.
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