aseprite/data/widgets/palette_size.xml

<!-- Aseprite -->
<!-- Copyright (C) 2015-2018 by David Capello -->
<gui>
<window id="palette_size" text="@.title">
  <grid columns="3">
    <label text="@.number_of_colors" />
    <expr expansive="true" id="colors" magnet="true" />
    <box cell_align="horizontal" />

    <separator horizontal="true" cell_hspan="3" />

    <box horizontal="true" homogeneous="true" cell_hspan="3" cell_align="right">
      <button text="@general.ok" closewindow="true" id="ok" magnet="true" minwidth="60" />
      <button text="@general.cancel" closewindow="true" />
    </box>
  </grid>
</window>
</gui>