Overhaul the stylesheet with tokens and dark mode

The old sheet had no overflow rules, so wide code, diff, blame and
stats blocks scrolled the whole page sideways on a phone. The classic
layout, badge colours and age shading are kept.

2 files changed, 466 insertions, 225 deletions

diff --git a/assets/cgit.css b/assets/cgit.css
index e02d551..73b61f1 100644
--- a/assets/cgit.css
+++ b/assets/cgit.css
This diff is too large to be rendered inline. View it on its own page.
diff --git a/source/ui-shared.c b/source/ui-shared.c
index 757e328..83454fe 100644
--- a/source/ui-shared.c
+++ b/source/ui-shared.c
@@ -813,7 +813,7 @@ void cgit_print_docstart(void)
 	}
 
 	html(cgit_doctype);
-	html("<html lang='en'>\n");
+	html("<html lang='en' class='cgit-standalone'>\n");
 	html("<head>\n");
 	html("<meta charset='utf-8'/>\n");
 	html("<meta name='viewport' content='width=device-width, initial-scale=1'/>\n");