Any area, divided vertically, looks narrower.  That's why vertical design lines are such a powerful way to look taller and trimmer in your clothes.  A vertical can extend the length of your entire look, or can be used just on the parts you'd like to visually narrow. 

The vertical strip of red sweater showing between the front edges of Donna's jacket minimize the width of her upper body and make her inverted triangle figure look more balanced.  NOTE: If you're going to wear a jacket unbuttoned, be sure it's large enough that you could button it if you chose to.  Otherwise it will look too small, and you'll look heavier by comparison. 

Here are other examples of slimming vertical design lines - some of them possibly surprising:

           * Draped panels, center pleats, topstitched center seam or slit, or center trim panel as shown above ... PLUS ...

           * A front band on a shirt-dress, blouse or jacket -- especially if the band is a contrast color or outlined with piping or trim.

          * A row of contrasting buttons.

          * Pressed-in creases or pleats in trousers.

          * A center inverted pleat in a skirt.

          * The draped front edge of a cascade sweater.

          * A jacket with a low button stance, expecially if the lapels are narrow.

          * Soft folds in a mid-calf full skirt (if the fabric falls close to the body).

          * The overlap edge of a wrap skirt.

          * A Color Column - top and bottom that match in color.

          * Hosiery in a similar color to the pant or skirt.

But even a detail as seemingly fail-safe as vertical lines needs to be used with care.  In the two skirts below, the narrowly-spaced vertical seams move the eye up and down. but the more widely-spaced seams actually move the eye side to side between them, creating an unintended widening effect --  Oops!

What vertical details can your find or create in your current wardrobe?