BUG/MINOR: stats: define the description' background color in dark color scheme

Shawn Heisey reported that the proxy's description was unreadable in dark
color scheme. This is because the text color is changed in the table but
not the cell's background.

This should be backported to 2.5.
diff --git a/src/stats.c b/src/stats.c
index 5379332..2d1a33c 100644
--- a/src/stats.c
+++ b/src/stats.c
@@ -3356,6 +3356,7 @@
 	              " a.lfsb:visited {color: #e8e6e3; text-decoration: none;}\n"
 	              " a.lfsb:hover {color: #b5afa6; text-decoration: none;}\n"
 	              " table.tbl th.empty { background-color: #181a1b; }\n"
+	              " table.tbl th.desc { background: #181a1b; }\n"
 	              " table.tbl th.pxname { background-color: #8d0033; color: #ffff46; }\n"
 	              " table.tbl th { border-color: #808080; }\n"
 	              " table.tbl td { border-color: #808080; }\n"