Tweak top-nav button styles

This assumes the active button is the one without a 'flat' class.

src/app/top-nav/top-nav.template.html

@@ -10,7 +10,7 @@
     </h1>
 
     <div class="buttons">
-        <button class="flat active">Boards</button>
+        <button>Boards</button>
         <button class="flat">Settings</button>
         <button class="flat">Logout (username)</button>
     </div>

src/scss/_nav-top.scss

@@ -23,20 +23,18 @@
         float: right;
         margin-top: -2.2em;
 
+        button {
+            transition: background-color .3s;
+        }
+
         .flat {
             background-color: lighten($color-background, 3%);
             color: $color-primary;
-            transition: background-color .5s;
 
             &:hover {
-                background-color: lighten($color-background, 7%);
+                background-color: lighten($color-background, 9%);
             }
         }
-
-        .active {
-            background-color: $color-primary;
-            color: $color-text-button;
-        }
     }
 }