add responsive grids css rule to cssgrids and update build.json

src/cssgrids/build.json

@@ -16,6 +16,13 @@
             "cssfiles": [
                 "cssgrids-base.css"
             ]
+        },
+        "cssgrids-responsive": {
+            "cssfiles": [
+                "cssgrids-base.css",
+                "cssgrids-units.css",
+                "cssgrids-responsive-base.css"
+            ]
         }
     }
 }

src/cssgrids/css/cssgrids-responsive-base.css

@@ -0,0 +1,44 @@
+.yui3-g-responsive {
+    letter-spacing: -0.31em;
+    *letter-spacing: normal;
+    word-spacing: -0.43em;
+}
+.yui3-g-responsive img {
+    max-width: 100%;
+}
+
+@media (min-width:980px) { 
+    .yui3-visible-phone {
+        display: none;
+    }
+    .yui3-visible-tablet {
+        display: none;
+    }
+    .yui3-hidden-desktop {
+        display: none;
+    }
+}
+@media (max-width:480px) { 
+    .yui3-g-responsive > [class ^= "yui3-u"] {
+        width: 100%;
+    }
+}
+@media (max-width:767px) { 
+    .yui3-g-responsive > [class ^= "yui3-u"] {
+        width: 100%;
+    }
+    .yui3-hidden-phone {
+        display: none;
+    }
+    .yui3-visible-desktop {
+        display: none;
+    }
+}
+@media (min-width:768px) and (max-width:979px) { 
+    .yui3-hidden-tablet {
+        display: none;
+    }
+    .yui3-visible-desktop {
+        display: none;
+    }
+}

src/cssgrids/meta/cssgrids.json

@@ -19,6 +19,19 @@
         "type": "css"
     },
 
+    "cssgrids-responsive": {
+        "requires": [
+            "cssgrids",
+            "cssgrids-responsive-base"
+        ],
+
+        "optional": [
+            "cssreset",
+            "cssfonts"
+        ], 
+        "type": "css"
+    },
+
     "cssgrids": {
         "optional": [
             "cssreset",