Try Merriweather as serif font.

services/web/public/stylesheets/components/navbar.less

@@ -384,7 +384,7 @@
     position: absolute;
     top: 5px;
     bottom: 5px;
-    width: 160px;
+    width: 180px;
     padding: 0;
     background-image: url('/img/brand/logo-horizontal.svg');
     background-size: contain;

services/web/public/stylesheets/core/variables.less

@@ -51,10 +51,11 @@
 
 @import url(https://fonts.googleapis.com/css?family=Open+Sans:300,400,600,700);
 //@import url(https://fonts.googleapis.com/css?family=PT+Serif:400,600,700);
-@import url(https://fonts.googleapis.com/css?family=PT+Serif:400,400i,700,700i);
+//@import url(https://fonts.googleapis.com/css?family=PT+Serif:400,400i,700,700i);
+@import url(https://fonts.googleapis.com/css?family=Merriweather:400,400i,700,700i);
 
 @font-family-sans-serif:  "Open Sans", sans-serif;
-@font-family-serif:       "PT Serif", serif;
+@font-family-serif:       "Merriweather", serif;
 //** Default monospace fonts for `<code>`, `<kbd>`, and `<pre>`.
 @font-family-monospace:   Menlo, Monaco, Consolas, "Courier New", monospace;
 @font-family-base:        @font-family-sans-serif;