Try this, it's made without testing.. if it's not working, i'll fix it once i'm back at the pc
<panel>
<attachment_group class="vertical_arrange" vertical_alignment="top,extend" />
<!-- HEADER -->
<widget class="link_button" section="Psta" auto_size="vertical" alignment="top,centre_x">
<translation id="text" translation_id="402385" type="use" value="Player Traits" />
</widget>
<container>
<layout class="arrange_vertical_attachment" alignment="top,extend" offset="0" gap="0"/>
<layout class="stick_to_sides_attachment" alignment="horizontal" apply_to_children="true" inset="0"/>
<widget class="preferred_moves_panel" auto_size="vertical" file="player/player information preferred moves" id="pfmp">
<record id="object_property" get_property="objt" set_property="objt" />
</widget>
</container>
</panel>