dark-mode: invert the images in the About section

These images simply have too-dark labels otherwise.

The proper solution would likely involve a separate set of images in
that section, specifically targeting dark mode, with a
specially-designed color palette. But I am not the person you want to do
that, there are experts for this kind of stuff out there in the world, I
ain't one of them.

Signed-off-by: Johannes Schindelin <[email protected]>

Author: dscho

assets/sass/dark-mode.css

@@ -75,6 +75,11 @@
                 filter: brightness(.6) contrast(1.2);
             }
 
+            // the images in the About section would be too dark
+            body#about img:not([alt="Git"]) {
+                filter: brightness(0.9) contrast(0.6) invert(1);
+            }
+
             a.subtle-button {
                 background-image: linear-gradient(#555555, #777777);
                 border-top: solid 1px #333333;