Grid cell gaps on the list item, not the inner box

Themes paint the chip on the gridview > child node, which spans the
whole cell: margins on the inner box only inset the content inside the
chip, so inter-cell gaps never widened (visible in beta.16). Put the
uniform 3px margins on the ListItem itself; restore the box margins.

Author: houssemko

src/gallery_grid.rs

@@ -98,6 +98,15 @@ impl GalleryGrid {
                 let list_item = object
                     .downcast_ref::<gtk4::ListItem>()
                     .expect("setup handler gets a ListItem");
+                // The gaps between grid cells (GridView has no spacing
+                // properties) are margins on the list item: themes paint
+                // the chip on the `gridview > child` node, which spans the
+                // whole cell, so margins on the inner box only move content
+                // inside the chip. 3px uniform = 6px gap between cells.
+                list_item.set_margin_top(3);
+                list_item.set_margin_bottom(3);
+                list_item.set_margin_start(3);
+                list_item.set_margin_end(3);
                 let label = gtk4::Label::builder()
                     .ellipsize(pango::EllipsizeMode::End)
                     .max_width_chars(24)
@@ -110,17 +119,13 @@ impl GalleryGrid {
                 let check = gtk4::CheckButton::new();
                 check.set_can_target(false);
                 check.set_focusable(false);
-                // The margins create the gaps between grid cells (GridView
-                // has no spacing properties; only the space between cells,
-                // both axes, at one uniform value) and keep focus rings
-                // from clipping at the scroll edges.
+                // The margins keep focus rings from clipping at the scroll
+                // edges.
                 let cell = gtk4::Box::builder()
                     .orientation(gtk4::Orientation::Horizontal)
                     .spacing(6)
-                    .margin_top(3)
-                    .margin_bottom(3)
-                    .margin_start(3)
-                    .margin_end(3)
+                    .margin_top(2)
+                    .margin_bottom(2)
                     .focusable(true)
                     .build();
                 cell.append(&check);