1) .css (Cascading Style Sheet)
2) .psd (PhotoShop)
3) .fla (Flash)
4) .swf (SWiSH)

1) What is .css?
CSS stands for Cascading Style Sheets. It defines how to display HTML elements in a web page. Web templates with CSS layout makes it easier for user to do a global design changes.

2) What is .psd?
A PSD file is a layered, easy to modify image file. You can do just about any kind of customization using Adobe Photoshop. You can change text, image colors, add your own photos to your web design template and save optimized image data for web.

3) What is .fla?
.FLA file is a source Flash file that contains all animation and graphics. .FLA file are editable using Flash editor software such as Macromedia Flash or SWiSH.

4) What is .swf?
SWF is a vector graphics file format produced by Flash software. It stands for Small Web Format and Shockwave Flash. SWF files contain compressed and uneditable applets or animations source.