try this

.dijitSelect .dijitButtonNode {width:16px !important;}
 dom-style.set(dojo.query('.dijitSelect')[0],'width',with);

try this

.dijitSelect .dijitButtonNode {
  width: 16px !important; 
}
 
dom-style.set(dojo.query('.dijitSelect')[0], 'width', with);

.dijitSelect .dijitButtonNode {width:16px !important;}

dom-style.set(dojo.query('.dijitSelect')[0],'width',with);

try this

.dijitSelect .dijitButtonNode {width:16px !important;}
 dom-style.set(dojo.query('.dijitSelect')[0],'width',with);