Is there a way to style Google Chrome default PDF viewer

Question

Is there a way to style google chrome default pdf view? I\'m trying to change the gray background color to white also make the scroller little bigger for mobile devices if possi

Answer 1

Update: Recent versions of Chrome seem to have moved the PDF viewer resources out of resources.pak and into the browser binary itself. It should still be possible to download the Chromium source, edit the files described below, and then recompile, but that's much more painful than simply hacking resources.pak. Thanks, Google.

As a matter of fact, there is a way, but we've got to get our hands dirty, and the process must be repeated every time we update Chrome. Still, to me, the effort is well worth it. I like to change the PDF viewer's background to white, so that when I activate the color-inverting Deluminate extension at night, I get a nice solid black background. It's so much easier on my eyes compared to the default background, which, when inverted, is blindingly bright.

The Chrome source tree contains thousands of HTML, JS, and CSS files that control the behavior and appearance of many parts of the browser, including the PDF viewer. When Chrome is built, these "resources" are bundled together into a single file, resources.pak, which the browser unpacks into memory during startup. What we need to do is unpack resources.pak on disk, edit the files that style the PDF viewer, and then repack the bundle.

The first thing we need is a tool that can unpack resources.pak. The only one that I know of is ChromePAK-V5. It's written in Go, so we need that to build it. We also need to install a build-time dependency called go-bindata. Here's how I went about it:

cd ~/code/chrome
go get -u github.com/jteeuwen/go-bindata/...
git clone https://github.com/shuax/ChromePAK-V5.git
cd ChromePAK-V5
~/go/bin/go-bindata -nomemcopy -o assets.go assets
go build
cd ..

Now that we've got the binary ChromePAK-V5/ChromePAK-V5, we can use it to unpack resources.pak. In my case, running Chromium on Linux, the file is located at /usr/lib/chromium/resources.pak, but it might be somewhere else for you. Once you've found it, copy it, make a backup, and unpack it:

cd ~/code/chrome
cp /usr/lib/chromium/resources.pak .
cp resources.pak resources.pak.bak
ChromePAK-V5/ChromePAK-V5 -c=unpack -f=resources.pak

At this point, the files we need will be located somewhere in the resources directory. Now, in the original Chrome source tree, these files all had sensible paths, such as chrome/browser/resources/pdf/pdf_viewer.js. Unfortunately, these original paths are not recorded in the resources.pak file. ChromePAK-V5 tries to be clever by using a table that maps the SHA1 hashes of resources files to their original paths, but over time, files change, along with their hashes, and ChromePAK-V5 can no longer recognize them. If a file is unrecognized, ChromePAK-V5 will unpack it to, e.g., resources/unknown/12345. And, in general, these numbers change from one Chrome release to the next. So, to find the files that we need to edit, we basically need to grep for "fingerprints" that identify them. Let's get started.

The background color of the PDF viewer is controlled by the file which, in the Chrome source tree, is named chrome/browser/resources/pdf/pdf_viewer.js. To find the file, grep inside resources/unknown for the string PDFViewer.BACKGROUND_COLOR. In my case, the file was unpacked at unknown/10282. Open this file, and change the line (at/near the end of the file) that sets PDFViewer.BACKGROUND_COLOR. I changed it to 0xFFFFFFFF, i.e., white (which becomes black under Deluminate).

Going further, we can also restyle the PDF viewer's toolbar. By default, the toolbar is dark, so it becomes obnoxiously bright under Deluminate. To fix that, we need to find chrome/browser/resources/pdf/elements/viewer-pdf-toolbar.html. I found it at unknown/10307 by grepping for shadow-elevation-2dp. What I did was to go to the #toolbar block and add filter: invert(100%);. Voila, no more blinding toolbar at night.

Finally, if we really want to go all the way, we can get rid of the brief "flash" of the original background color that occurs when loading a PDF. This color is controlled by chrome/browser/resources/pdf/index.css, which I found at unknown/10304 by grepping for viewer-page-indicator {. I changed the background-color property of body to white (i.e. black under Deluminate).

The hard part is now over. The final step is to repack the resources and overwrite the system resources.pak:

ChromePAK-V5/ChromePAK-V5 -c=repack -f=resources.json
sudo cp resources.pak /usr/lib/chromium       # or wherever yours should go

Now restart the browser and enjoy!