feat: DH-22800: Support Intersection 2D Window Resizing

packages/golden-layout/scss/goldenlayout-base.scss

@@ -39,6 +39,11 @@ $height6: 15px; // Appears 1 time
   user-select: none;
 }
 
+.lm_intersection_dragging,
+.lm_intersection_dragging * {
+  cursor: move !important;
+}
+
 // If a specific Pane is maximized
 .lm_maximised {
   position: absolute;
@@ -79,6 +84,32 @@ $height6: 15px; // Appears 1 time
       cursor: ew-resize;
     }
   }
+
+  // While part of an active 2D intersection (hover or drag), lift the line above
+  // pane content so an offset T/cross junction renders cleanly instead of being
+  // clipped by the neighbouring pane. Stays below the intersection handle
+  // (z-index 60) so the handle always wins pointer priority for 2D dragging.
+  &.lm_intersection_line {
+    z-index: 59;
+  }
+}
+
+// Intersection splitter: an invisible grab area at grid crossing points that
+// enables simultaneous (2D) resizing of rows and columns. The visible drag
+// affordance is the two perpendicular splitter lines themselves, which are
+// highlighted (via .lm_dragging) on hover and while dragging.
+.lm_intersection_splitter {
+  position: absolute;
+  z-index: 60;
+  pointer-events: auto;
+  cursor: move;
+
+  .lm_drag_handle {
+    position: absolute;
+    width: 100%;
+    height: 100%;
+    cursor: move;
+  }
 }
 
 // Pane Header (container of Tabs for each pane)

packages/golden-layout/scss/goldenlayout-dark-theme.scss

@@ -133,6 +133,13 @@ body:not(.lm_dragging) .lm_header .lm_tab:hover .lm_close_tab {
   }
 }
 
+// Intersection splitter (2D grid resize). The grab area is invisible; the drag
+// affordance is the two perpendicular splitter lines, which reuse the standard
+// .lm_splitter.lm_dragging highlight above.
+.lm_intersection_splitter {
+  background: transparent;
+}
+
 // Pane Header (container of Tabs for each pane)
 .lm_header {
   box-sizing: content-box; // golden-layout sets a js height using a content box model