columns : add variables for row and column gap

Author: cedric07

src/scss/06-blocks/core/_columns.scss

@@ -1,6 +1,13 @@
 .wp-block-columns {
+    --wp-block-columns-row-gap: var(--spacing--block-2);
+    --wp-block-columns-column-gap: #{get_gutter-width()};
+
     @include block-vertical-spacing();
 
+    row-gap: var(--wp-block-columns-row-gap);
+    column-gap: var(--wp-block-columns-column-gap) !important;
+    justify-content: space-between;
+
     .wp-block-column {
         &.has-background {
             padding: var(--spacing--block-1);
@@ -19,6 +26,10 @@
                 &:not(:only-child) {
                     flex-basis: 100% !important;
                 }
+
+                &:empty {
+                    display: none;
+                }
             }
         }
     }