fixe a z-index bug

src/css/Header.styl

@@ -3,7 +3,7 @@
   width 100%
   box-shadow shadow-bottom
   background mainColor
-  z-index 4
+  z-index 5
   &__logo
     &__img
       width 150px

src/css/Sidebar.styl

@@ -36,7 +36,7 @@ leftside()
   position relative
   transition all sidebar-animate-speed
   width sidebar-width
-  z-index 2
+  z-index 4
   &.sidebarclose
     width 0
   &__expand