1. Go –> App Folder –> Design –> frontend –> create OR copy exciting theme folder.
2. Copy base folder inside default theme content. And Paste your theme content inside.
3. GO –> Skin Folder –> frontend –> copy exiting skin folder –> and create your theme folder or copy exiting theme and rename.(ex: universial/universial
4. you want to change any widget css. copy base folder skin content to your skin folder inside.