Add overlay/content example

[arist0tl3]

Added an example I used to animate modal content in and apply an opacity transition to the overlay. If this is interesting I can look into adding to the /examples as well.

Acceptance Checklist:

• [x] The commit message follows the guidelines in CONTRIBUTING.md.
• [n/a] Documentation (README.md) and examples have been updated as needed.
• [n/a] If this is a code change, a spec testing the functionality has been added.
• [n/a] If the commit message has [changed] or [removed], there is an upgrade path above.

[diasbruno]

LEGIT. Obrigado, @arist0tl3!

[diasbruno]

The style is the "default style" that we use on the examples, right?

[arist0tl3]

@diasbruno

I think I understand what you were getting at -- just updated the example to use the default styles and note that transform will need to be removed in order for this example to work properly.

[diasbruno]

Great. Is there a bug on the styles of the examples?

[arist0tl3]

No, but if I try to do this:

.ReactModal__Content {
  transform: translate(-50%, 150%);
  transition: transform 800ms ease-in-out;
}

.ReactModal__Content--after-open {
  transform: translate(-50%, -50%);
}

.ReactModal__Content--before-close {
  transform: translate(-50%, 150%);
}

the inline style will take precedence. It felt better to suggest removing that inline style and define it instead as a css rule vs keeping it as is and adding !important to the rules above.

[arist0tl3]

Took a stab at wording it; lmk if it does/doesn't make sense lol

[diasbruno]

Everything looks good. Thanks so much for taking the time to help with the docs. Grande Lavoro. :tada: Grazie mille.