README architectural diagram graphic displays poorly in common "dark mode" black backgrounds

Describe the bug When viewing README.md on a typical "dark mode" browser setup, i.e., one that utilizes a background-color: #000 for black backgrounds, or perhaps in general on any other similarly dark color, key elements of the very first architectural diagram graphic become unreadable.

Cause/fix The illegibility atop dark colors is clearly caused by the dark (black) font used on top of transparent pixels in the graphic. The cleanest, most robust solution would be to embed a color in place of those transparent pixels that is appropriately contrasting with the dark font, for example white.

Steps to Reproduce

1. Force "dark mode" in your browser, or view the graphic atop a black background (such as by momentarily applying background-color: #000 CSS via your browser's dev tools).
2. Note the unreadable portions circled in red in this annotated screenshot: