Revert "dashboard: remove content-visibility CSS to fix log windows…

… not being scrolled to the bottom after expanding them in Chrome"

This reverts commit c99d488.

This regressed performance in Chrome when having all the log windows expanded
and looking at the top of the page: memory footprint went from 214MB -> 442MB
and CPU time went from 1m18s to 1m52s.

dashboard/dashboard.html

@@ -227,10 +227,12 @@
 	box-shadow: 4px 4px 17px 0px #0000001c;
 	overscroll-behavior: contain;
 	contain: strict;
+	content-visibility: auto;
 }
 
 .log-window-hidden {
 	display: none;
+	content-visibility: hidden;
 }
 
 .log-window-stopped {