Added Sans-Serif theme.

model/theme.go

@@ -9,8 +9,9 @@ import "github.com/miniflux/miniflux/errors"
 // Themes returns the list of available themes.
 func Themes() map[string]string {
 	return map[string]string{
-		"default": "Default",
-		"black":   "Black",
+		"default":   "Default",
+		"black":     "Black",
+		"sansserif": "Sans-Serif",
 	}
 }
 

ui/static/css/sansserif.css

@@ -0,0 +1,11 @@
+body,
+.entry-content,
+.entry-content blockquote,
+.entry-content q {
+    font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, "Helvetica Neue", Arial, sans-serif, "Apple Color Emoji", "Segoe UI Emoji", "Segoe UI Symbol";
+}
+
+.entry-content {
+    font-size: 1.17em;
+    font-weight: 400;
+}