Default standard width for the infobar is 140px

Infobar width.
width = infobar widthleft = -(infobar width + infobar right margin)
If you're changing this values, don't forget to change following values too:
'margin-left' in '#page_content' 
'margin-left' in '#main_container'

Example changing infobar width to 180px

/interface_{custom}/common/style.css

#infobar_main {
	width: 180px;
	left: -185px;
}
 
#main_container {
	/* margin-left must be equal to negative infobar width with margin */
        margin-left: 185px;
}
 
#page_content{
	/* margin-left must be equal to negative infobar width */
        margin-left: -180px;
}