[IMP] mrp: bigger folding arrow on BoM cost view

...Only on mobile device.

closes odoo/odoo#38162

Signed-off-by: Simon Lejeune (sle) <sle@openerp.com>

addons/mrp/static/src/scss/mrp_bom_report.scss

@@ -31,6 +31,14 @@
             }
         }
     }
+
+    @include media-breakpoint-down(sm) {
+        .o_mrp_bom_report_line {
+            & .fa-caret-down, & .fa-caret-right {
+                font-size: 2em;
+            }
+        }
+    }
 }
 
 .o_mrp_bom_report_buttons {