@PeterJones keeping the 2 Listboxes might be OK as well since I have mocked it recently.
NppListToCombo2.png
Left side and center same as my previous post. The right side displays 2 listboxes with 8 items per list being visible. Either of the 2 alternatives appear wider as can be seen in the image.
Here is the AutoIt3 sources if anyone wants to play with them. Just need the AutoIt3 interpreter which can get from downloading the Zip file and extract AutoIt3.exe or AutoIt3_x64.exe.
; about: With 1 ComboBox and 1 Listbox.
Global Const $CBS_DROPDOWNLIST = 0x3
Global Const $GUI_EVENT_CLOSE = -3
Global Const $WS_VSCROLL = 0x00200000
Global Const $WS_CAPTION = 0x00C00000
GUICreate('Style Configurator', 750, 405, -1, -1, $WS_CAPTION)
GUICtrlCreateLabel('Select theme:', 67, 15)
GUICtrlCreateCombo('Default (stylers.xml)', 142, 15, 160, Default, $CBS_DROPDOWNLIST)
GUICtrlCreateGroup('', 10, 45, 250, 345)
GUICtrlCreateLabel('Language:', 20, 60)
GUICtrlCreateCombo('Global Styles', 20, 85, 230, Default, $CBS_DROPDOWNLIST)
GUICtrlSetData(Default, 'ActionScript|ADA|ASN.1|ASP')
GUICtrlCreateLabel('Style:', 20, 120)
GUICtrlCreateList('Default Style', 20, 145, 230, 180, $WS_VSCROLL)
GUICtrlSetData(Default, 'Indent guideline style|Brace highlight style|Bad brace colour' & _
'|Current line background|Selected text colour|Multi-selected text color' & _
'|Caret colour|Multi-edit carets color|Edge colour|Line number margin' & _
'|Bookmark margin|Change History margin|Change History modified' & _
'|Change History revert modified|Change History revert origin' & _
'|Change History saved|Fold|Fold active' & _
'|1|2|3|4|5|6|7|8|9|10|11|12|13|14|15|16|17|18|19|20')
$idExit = GUICtrlCreateButton('Exit', 650, 365, 80)
GUISetState()
While 1
Switch GUIGetMsg()
Case $GUI_EVENT_CLOSE, $idExit
Exit
EndSwitch
WEnd
; about: With 2 Listboxes
Global Const $CBS_DROPDOWNLIST = 0x3
Global Const $GUI_EVENT_CLOSE = -3
Global Const $WS_VSCROLL = 0x00200000
Global Const $WS_CAPTION = 0x00C00000
GUICreate('Style Configurator', 750, 405, -1, -1, $WS_CAPTION)
GUICtrlCreateLabel('Select theme:', 67, 15)
GUICtrlCreateCombo('Default (stylers.xml)', 142, 15, 160, Default, $CBS_DROPDOWNLIST)
GUICtrlCreateGroup('', 10, 45, 250, 345)
GUICtrlCreateLabel('Language:', 20, 60)
GUICtrlCreateList('Global Styles', 20, 80, 230, 120, $WS_VSCROLL)
GUICtrlSetData(Default, 'ActionScript|ADA|ASN.1|ASP|Assembly|AutoIt|AviSynth' & _
'|1|2|3|4|5|6|7|8|9|10|11|12|13|14|15|16|17|18|19|20')
GUICtrlCreateLabel('Style:', 20, 195)
GUICtrlCreateList('Default Style', 20, 215, 230, 120, $WS_VSCROLL)
GUICtrlSetData(Default, 'Indent guideline style|Brace highlight style|Bad brace colour' & _
'|Current line background|Selected text colour|Multi-selected text color' & _
'|Caret colour|Multi-edit carets color|Edge colour|Line number margin' & _
'|Bookmark margin|Change History margin|Change History modified' & _
'|Change History revert modified|Change History revert origin' & _
'|Change History saved|Fold|Fold active' & _
'|1|2|3|4|5|6|7|8|9|10|11|12|13|14|15|16|17|18|19|20')
$idExit = GUICtrlCreateButton('Exit', 650, 365, 80)
GUISetState()
While 1
Switch GUIGetMsg()
Case $GUI_EVENT_CLOSE, $idExit
Exit
EndSwitch
WEnd
I didn’t type the full list of items as it is just mocking the Style Configurator Dialog for display purposes.