sysprof: make the sidebar a bit nicer w/ traceables

src/libsysprof-gtk/style.css

@@ -99,3 +99,7 @@ tracks row {
 tracks row track info {
   padding: 1px 0 0 0;
 }
+
+.utility .view {
+  background: transparent;
+}

src/sysprof/sysprof-samples-section.ui

@@ -75,6 +75,9 @@
     </child>
     <property name="utility">
       <object class="AdwToolbarView">
+        <style>
+          <class name="utility"/>
+        </style>
         <child type="top">
           <object class="AdwHeaderBar">
             <property name="title-widget">