Any styles you’ve applied (such as a strokes, border radius or shadow sizes) will stay the same when you resize a layer. To have them scale proportionately with your layer size, head to Layer > Transform > Scale… or press ⌘K.
In the SCALE LAYERS controls in the DETAILS tab of the Inspector, you can choose whether your layer will resize from its center, sides or corners. You can see a preview of all your changes as you go in the Canvas.