Improve navbar UX

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

app/assets/stylesheets/sections/nav.scss

@@ -36,8 +36,7 @@
       &.active {
         a {
           color: #333;
-          font-weight: bolder;
-
+          font-weight: bold;
           &:after {
             content: '';
             display: block;
@@ -56,7 +55,20 @@
 
       &:hover {
         a {
-         color: $style_color;
+          color: $link_color;
+          &:after {
+            content: '';
+            display: block;
+            position: relative;
+            bottom: 8px;
+            left: 50%;
+            width: 0;
+            height: 0;
+            border-color: transparent transparent #29b transparent;
+            border-style: solid;
+            border-width: 6px;
+            margin-left: -6px;
+          }
         }
       }
 
@@ -73,7 +85,7 @@
     a {
       display: block;
       text-align: center;
-      font-weight: normal;
+      font-weight: 500;
       height: 38px;
       line-height: 34px;
       color: #777;