UI improvements for scope boxes

[forrestbao]

I suggest

1. Change the header bar to what pod's look like. No explicit header bar like in Windows 95. No red dot.
2. Do not use pink infill. Use light blue.
3. Add a delete button. Once clicked, it will remove the scope box.

@lihebi @nibilin33 what do you say?

[lihebi]

Sounds good.

[nibilin33]

to make it look like this?

@forrestbao

[forrestbao]

Please keep the text scope in the head though. Need to distinguish a scope from a code cell.
@nibilin33 please do not delete the line for color filling. Just comment out, set it to transparent, or leave the fill color as white. I now feel fill might be a good visual prompt to users. We will need to do some A/B test.

@lihebi What's your opinion?

[lihebi]

We probably need to involve a designer here.