Fix image color inversion w/ CSS

Change-Id: Ic156d24cb41af68c6904b5b9fc335531004ae755
diff --git a/css/style.css b/css/style.css
index 7556945..b36241e 100644
--- a/css/style.css
+++ b/css/style.css
@@ -19,6 +19,10 @@
   transition: background .15s, box-shadow .1s;
 }
 
+.navbar-brand-image {
+  filter: invert(100%);
+}
+
 #wrap_a {
   max-width: 800px;
   margin: 0 auto;