/usr/share/afterstep/desktop/buttons/glass-menu-pressed is in afterstep-data 2.2.12-6.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 | <hsv id="btn_back_active" hue_offset="$ascs.Active.hue"
saturation_offset="$ascs.Active.saturation-30"
value_offset="$ascs.Active.value-60">
<img src="bars/btn_back_glass_red"/>
</hsv>
<composite merge="clip">
<recall srcid="btn_back_active"/>
<tile x="5" y="5" tint="#FFFFFF">
<scale width="14" height="11">
<img src="dots/menu_medium"/>
</scale>
</tile>
<tile tint="#6f7f7f7f" x="0" y="0">
<recall srcid="btn_back_active"/>
</tile>
</composite>
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