sudo gedit /usr/share/themes/Adwaita/metacity-1/metacity-theme-3.xml

<frame_geometry name="max" has_title="false" title_scale="medium" parent="normal" rounded_top_left="false" rounded_top_right="false">

　　<distance name="left_width" value="0" />

　　<distance name="right_width" value="0" />

　　<distance name="left_titlebar_edge" value="0"/>

　　<distance name="right_titlebar_edge" value="0"/>

　　<distance name="title_vertical_pad" value="0"/> <!-- 

　　This needs to be 1 less then the

　　title_vertical_pad on normal state

　　or you'll have bigger buttons -->

　　<border name="title_border" left="10" right="10" top="0" bottom="0"/>

　　<border name="button_border" left="0" right="0" top="0" bottom="0"/>

　　<distance name="bottom_height" value="0" />

</frame_geometry>

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