Add nav, Enhance tabs

sass/layout/header.sass

@@ -3,16 +3,18 @@
   background: $white
   display: flex
   line-height: 24px
+  min-height: $header-height
   position: relative
   text-align: center
   z-index: 2
   .container
     align-items: stretch
     display: flex
+    min-height: $header-height
     width: 100%
   // Modifiers
   &.has-shadow
-    box-shadow: 0 1px 2px rgba($black, 0.1)
+    box-shadow: 0 2px 3px rgba($black, 0.1)
   // Responsiveness
   +mobile
     .container
@@ -62,13 +64,6 @@ a.header-item
   &.is-active
     color: $link-active
 
-.header-icon
-  +fa(14px, 24px)
-  color: $text
-  margin: 0 5px
-  &:hover
-    color: $link-hover
-
 .header-tab
   align-items: center
   border-bottom: 1px solid transparent