The search results are currently pushed to the left side of the window. This leaves a lot of empty space, and means that the results are divorced from the search box.

Placing the results in a column which is centered under the search bar would help a lot.

I can acheive the desired result in GtkInspector by changing the following properties on the GdMainListView which contains the search results:

halign: center
width-request: 530

And then changing the CSS with:

.content-view { background-color: @theme_bg; }