dropdown listbox arrow change size?

When you have selected your dropdown list go in the "layout" window/palette and change the different values there (axes, borders...).

Not sure the arrow's appearance will significantly change when only the width is modified.
The dropdown list should certainly be changed in its height too.

ps: your link does not load in my browser.

Well if I change width of my dropdown-list box the arrow size never changes. It 's the same size as default when you insert new dropdown-list.

Height can be changed but how do I change the width? I wanted to make control easy to read and it's stupid that the part user must click on is so small isn't it?

Height and width can both be managed in the "layout" palette.
(shortcut is Maj+F9 / or go in the "Window" menu and select it there)

Dropdown list is an object and objects parameters are available in the "object" and/or "layout" palettes.

Anyway, to action the list it is not necessary to click on the arrow, by just clicking on the entire field (the dropdown button list itself) it willl be open down (give it a try using the PDF preview).

But there is no control for "arrow size" like there is for checkbox size.

The arrow size or look can't be changed.