Ответ: Бордер у кнопки
По поводу бордера:
To create button rollover effects
In some cases, you may want the button area to be invisible until the mouse pointer is moved over it. One way to achieve this effect is to apply an image to the Rollover state in the States palette.
Create the first button that will act as the hot spot.
Create the second button that will be displayed during rollover. You may want to place an image and then convert it to a button.
You can also create a button that displays a second button. This is especially useful if you want one button to act as a “hot spot” area that displays a larger image, or an image in a different area. For example, when you move a pointer over a map, an image could be displayed that represents a region, and the image could disappear when the pointer moves away from the region.
RTFM