For people looking how to change button icons at bottom of the screen.
Add this lines in your main "theme.xml"
<view name="menu, system, basic, detailed">
<helpsystem name="help">
<iconColor></iconColor>
<iconUpDown></iconUpDown>
<iconLeftRight></iconLeftRight>
<iconUpDownLeftRight></iconUpDownLeftRight>
<iconA></iconA>
<iconB></iconB>
<iconX>/iconX>
<iconY></iconY>
<iconL></iconL>
<iconR></iconR>
<iconStart></iconStart>
<iconSelect></iconSelect>
<fontSize></fontSize>
<textColor></textColor>
</helpsystem>
just add your color, path of your files (.svg, png...) or font size in each properties.
