Merge pull request #8006 from aristath/3.0.0-wip

using screen-size variables for grids

less/grid.less

@@ -39,21 +39,21 @@
 // Responsive: Tablets and up
 @media screen and (min-width: @screen-tablet) {
   .container {
-    max-width: 728px;
+    max-width: @container-tablet;
   }
 }
 
 // Responsive: Desktops and up
 @media screen and (min-width: @screen-desktop) {
   .container {
-    max-width: 940px;
+    max-width: @container-desktop;
   }
 }
 
 // Responsive: Large desktops and up
 @media screen and (min-width: @screen-large-desktop) {
   .container {
-    max-width: 1170px;
+    max-width: @container-large-desktop;
   }
 }
 

less/variables.less

@@ -403,6 +403,19 @@
 @screen-large-desktop:       @screen-large;
 
 
+// Container sizes
+// --------------------------------------------------
+
+// Small screen / tablet
+@container-tablet:          728px;
+
+// Medium screen / desktop
+@container-desktop:         940px;
+
+// Large screen / wide desktop
+@container-large-desktop:   1170px;
+
+
 // Grid system
 // --------------------------------------------------