Update _position.scss

Created by: semblu

responsive 'fixed-top' & 'fixed-bottom'. Change of JS might be needed to prevent adding padding-right on '.fixed-top .fixed-lg-none' when 'body.modal-open'.

scss/helpers/_position.scss

-// Shorthand
-
-.fixed-top {
-  position: fixed;
-  top: 0;
-  right: 0;
-  left: 0;
-  z-index: $zindex-fixed;
-}
-
-.fixed-bottom {
-  position: fixed;
-  right: 0;
-  bottom: 0;
-  left: 0;
-  z-index: $zindex-fixed;
-}
-
-// Responsive sticky top
 @each $breakpoint in map-keys($grid-breakpoints) {
   @include media-breakpoint-up($breakpoint) {
     $infix: breakpoint-infix($breakpoint, $grid-breakpoints);
@@ -26,5 +7,27 @@
       top: 0;
       z-index: $zindex-sticky;
     }
+	.fixed#{$infix}-top {
+	  position: fixed;
+	  top: 0;
+	  right: 0;
+	  left: 0;
+	  z-index: $zindex-fixed;
+	}
+
+	.fixed#{$infix}-bottom {
+	  position: fixed;
+	  right: 0;
+	  bottom: 0;
+	  left: 0;
+	  z-index: $zindex-fixed;
+	}
+	.fixed#{$infix}-none {
+	  position: initial;
+	  right: initial;
+	  bottom: initial;
+	  left: initial;
+	  z-index: initial;
+	}
   }
 }