Add missing layout=columns sccs

resource/support/decker.scss

@@ -303,12 +303,28 @@ body {
                         column-rule-style: none;
                         padding-left: 0.7em;
                         margin-left: -0.7em;
+                    }
 
-                        >* {
-                            break-inside: avoid-column;
-                        }
+                    &.box {
+                        break-inside: avoid-column;
                     }
 
+                    &.multi-column-row {
+                        display:flex;
+                        flex-flow: row nowrap;
+
+                        div.column {flex: 1 1 0%;}
+                        div.column[grow="1"] {flex-grow:1;}
+                        div.column[grow="2"] {flex-grow:2;}
+                        div.column[grow="3"] {flex-grow:3;}
+                        div.column[grow="4"] {flex-grow:4;}
+                        div.column[grow="5"] {flex-grow:5;}
+                        div.column[grow="6"] {flex-grow:6;}
+                        div.column[grow="7"] {flex-grow:7;}
+                        div.column[grow="8"] {flex-grow:8;}
+                        div.column[grow="9"] {flex-grow:9;}
+                    }
+                                        
                     /////////////////////////////////////////////
                     // Video
                     /////////////////////////////////////////////

test/decks/column-deck.md

 ---
-css:
-- 'columns.css'
 history: True
 ---
 

test/decks/columns.css

-div.css-columns {
-    column-count: 2;
-    column-gap: 1em;
-    column-rule-style: none;
-}
-
-div.box {
-    break-inside: avoid-column;
-}
-
-div.multi-column-row {
-    display:flex;
-    flex-flow: row nowrap;
-}
-
-div.multi-column-row > div.column {flex: 1 1 0%;}
-div.multi-column-row > div.column[grow="1"] {flex-grow:1;}
-div.multi-column-row > div.column[grow="2"] {flex-grow:2;}
-div.multi-column-row > div.column[grow="3"] {flex-grow:3;}
-div.multi-column-row > div.column[grow="4"] {flex-grow:4;}
-div.multi-column-row > div.column[grow="5"] {flex-grow:5;}
-div.multi-column-row > div.column[grow="6"] {flex-grow:6;}
-div.multi-column-row > div.column[grow="7"] {flex-grow:7;}
-div.multi-column-row > div.column[grow="8"] {flex-grow:8;}
-div.multi-column-row > div.column[grow="9"] {flex-grow:9;}

test/decks/rendered-code-deck.md

 ---
-css: 'columns.css'
 history: True
 ---