User CP Message Width 
$stylevar[messagewidth_usercp]

This StyleVar is used to control the width of message input text boxes within the User Control Panel (such as the input area for the Private Message posting page).

Its functionality is identical to that of $stylevar[messagewidth], but it allows the width of the navigation panel in the User Control Panel to be taken into account.

The red arrow indicates the width controlled by this StyleVar:

For a discussion of the values this StyleVar will accept, see the page relating to the Message Area Width StyleVar $stylevar[messagewidth].
User Contributed Notes: User CP Message Width Add a Comment