The text in the 'show ground and selected layer' field in the options menu covers the number and arrows, so I can't modify them.
Thanks.
1. Download nightly from here (http://nightly.simutrans-germany.com/index.php?lang=en) because in official release is not included what is described in point 2
2. In right bottom corner of this dialogue is drag and pull button in form of striped corner (like on minimap) - and with this you can expand dialogue to size in what you would can change number of selected layer to view.