Add nav, Enhance tabs

sass/elements/button.sass

@@ -18,7 +18,7 @@
 
 .button
   +control
-  +unselectable
+  @extend .unselectable
   justify-content: center
   padding-left: 10px
   padding-right: 10px
@@ -95,8 +95,6 @@
   &[disabled],
   &.is-disabled
     opacity: 0.5
-  &.is-flexible
-    height: auto
   &.is-fullwidth
     display: block
     width: 100%

sass/elements/other.sass

@@ -1,5 +1,5 @@
 .delete
-  +unselectable
+  @extend .unselectable
   -moz-appearance: none
   -webkit-appearance: none
   background: rgba($black, 0.2)
@@ -56,9 +56,9 @@
 .hamburger
   cursor: pointer
   display: block
-  height: 50px
+  height: $nav-height
   position: relative
-  width: 50px
+  width: $nav-height
   span
     background: $text
     display: block
@@ -92,9 +92,6 @@
         margin-left: -5px
         transform: rotate(-45deg)
         transform-origin: left bottom
-  +tablet
-    height: $header-height
-    width: $header-height
 
 .heading
   display: block
@@ -180,3 +177,11 @@
     .delete
       margin-left: 4px
       margin-right: -8px
+
+.unselectable
+  -webkit-touch-callout: none
+  -webkit-user-select: none
+  -moz-user-select: none
+  -ms-user-select: none
+  user-select: none
+