Question

I wonder if is possible to have inner shadow effect on only one corner not one side?

Roughly like below.

--------------------------
|                        |
|                        |
|                       -|
|                     ---|
|                  ------|<-shadows
|               ---------|
--------------------------

Thank you very much for your advice.

Answer 1

You could make the shadow a gradient… From your background color to the color you want to achieve.
Use inset at your css to make the shadow appear inside the box and use http://www.colorzilla.com/gradient-editor/ to “create” the gradient hex code.