Add white black light dark colors, Fix button inverted

sass/layout/header.sass

@@ -1,6 +1,6 @@
 .header
   +clearfix
-  background: white
+  background: $white
   display: flex
   line-height: 24px
   position: relative
@@ -12,7 +12,7 @@
     width: 100%
   // Modifiers
   &.has-shadow
-    box-shadow: 0 1px 2px rgba(black, 0.1)
+    box-shadow: 0 1px 2px rgba($black, 0.1)
   // Responsiveness
   +mobile
     .container
@@ -128,7 +128,7 @@ a.header-item
 .header-menu
   // Responsiveness
   +mobile
-    box-shadow: 0 4px 7px rgba(black, 0.1)
+    box-shadow: 0 4px 7px rgba($black, 0.1)
     display: none
     .header-item
       border-top: 1px solid rgba($border, 0.5)