Issue number: Resolves#23942
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issue. -->
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## What is the current behavior?
<!-- Please describe the current behavior that you are modifying. -->
When an overlay is created (inserted in the DOM), but not presented, the
scroll gesture is prevented. This behavior comes from the
`connectedCallback` of `ion-backdrop`, where the gesture is prevented as
soon as the backdrop is inserted in the DOM.
This means in situations where a developer creates an overlay, but does
not present it immediately, the user cannot scroll. This is not desired.
## What is the new behavior?
<!-- Please describe the behavior or changes that are being added by
this PR. -->
- Scroll blocking behavior tied to the gesture has been removed from
`ion-backdrop` and implemented into the overlays directly.
- When an overlay is presented, scroll blocking is enabled on the `body`
element (the user cannot scroll on the main content).
- When the last presented overlay is dismissed, scroll blocking is
disabled on the `body` element (the user can scroll on the main
content).
## Does this introduce a breaking change?
- [x] Yes
- [ ] No
`ion-backdrop` no longer prevents scrolling on the main content when the
backdrop is either inserted into the DOM or removed from the DOM.
Developers using Ionic overlays do not need to migrate their
implementations.
Developers with custom overlays using `ion-backdrop` internally can
either use Ionic's gesture controller to disable scrolling when their
overlay is presented/dismissed or can manually add the
`backdrop-no-scroll` Ionic global class to the `body` element.
<!-- If this introduces a breaking change, please describe the impact
and migration path for existing applications below. -->
## Other information
<!-- Any other information that is important to this PR such as
screenshots of how the component looks before and after the change. -->
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- removes mode-less component classes from the internal CSS, use element instead
- adds mode specific classes `md` or `ios` for styling inside of shadow components
- adds e2e test that verifies mode classes exist on all ionic components, plus checks for specific classes that the components need for internal styling
fixes#17608
- updates components to use shadow DOM or scoped if they require css variables
- moves global styles to an external stylesheet that needs to be imported
- adds support for additional colors and removes the Sass loops to generate colors for each component
- several property renames, bug fixes, and test updates
Co-authored-by: Manu Mtz.-Almeida <manu.mtza@gmail.com>
Co-authored-by: Adam Bradley <adambradley25@gmail.com>
Co-authored-by: Cam Wiegert <cam@camwiegert.com>
