One of the great benefits to Illustrator artwork is the ability to scale it to any size without increasing the file size. Of course, frustration abounds when you increase or decrease a graphic but the stroke doesn't scale in synch with the fill. (By default, the stroke stays the same when scaled.) Not to worry, there's an easy fix to keep the elements scaling in proportion with each other; you just have to set the preference. Simply choose Edit > Preferences > General. Select the Scale Strokes and Effects check box, and click OK. And if you are using the Scale Tool, make sure to set the option there as well. Simply double-click on the Scale Tool, and in the resulting Scale dialog box select Scale Strokes & Effects.