1. Drop shadows, gradients, semi-transparent overlays, solid shapes, etc. can all be done with CSS. Don't use an image if you don't have to.
2. Use EVEN pixel dimensions when cutting (i.e. 242, NOT 241 or 243). This is so the browser does not round up or down when the image is placed within a div. Some browsers round up, some round down, so depending on the browser, your image will be off a pixel or two in some cases.

If you do not know how to export image assets from Photoshop, the following tutorials are great resources to learn how:

• https://helpx.adobe.com/photoshop/how-to/export-image-web.html - Basic methods for exporting layers
• https://helpx.adobe.com/photoshop/using/generate-assets-layers.html - More advanced workflows for generating assets