docs: update overlay components styling docs for V25

[web-padawan]

Updated Styling docs for overlay based components to use new part names.

[github-actions]

AI Language Review

In the updated "Popover" documentation file:

1. Consider replacing "kbd:[Space]" and "kbd:[Esc]" with a format that doesn't use square brackets or explicitly states they are keyboard inputs, as the square brackets might not render correctly in all contexts.

2. The consistency of providing the user with information about the components could be improved. For example, in the "Accessibility" section, ensure there are clear, detailed explanations for why certain ARIA roles are recommended or how they should be implemented.

3. In the "Typical Use Cases" section, additional context or explanation for each use case may be helpful to ensure users understand why each configuration is recommended.

Other than these points, the document is well-structured and provides comprehensive information about the component's functionality and styling.

[sissbruecker]

There are still several references to overlay elements in the component articles:

Date picker:

Today button:: `vaadin-date-picker-overlay+++<wbr>+++** [slot="today-button"]**`  
Cancel button:: `vaadin-date-picker-overlay+++<wbr>+++** [slot="cancel-button"]**`

Menu bar:

Separator element  `vaadin-menu-bar-overlay **[role="separator"]**`

MSBC:

Overlay element:: `vaadin-multi-select-combo-box-overlay`
Overlay background:: `vaadin-multi-select-combo-box-overlay+++<wbr>+++**::part(overlay)**`
Overlay content wrapper:: `vaadin-multi-select-combo-box-overlay+++<wbr>+++**::part(content)**`
Overlay in loading state:: `vaadin-multi-select-combo-box-overlay+++<wbr>+++**[loading]**`
Overlay loading indicator:: `vaadin-multi-select-combo-box-overlay+++<wbr>+++**::part(loader)**`

Popover:

The maximum width of popovers is limited to the width of the viewport, minus a small margin that can be customized with CSS by overriding the `inset` property of the `vaadin-popover-overlay` element.

Root element:: `vaadin-popover-overlay`


=== States

Non-modal:: `vaadin-popover-overlay+++<wbr>+++**[modeless]**`


=== Parts

Modality curtain (backdrop):: `vaadin-popover-overlay+++<wbr>+++**::part(backdrop)**`
Popover surface:: `vaadin-popover-overlay+++<wbr>+++**::part(overlay)**`
Content wrapper:: `vaadin-popover-overlay+++<wbr>+++**::part(content)**`
Arrow element:: `vaadin-popover-overlay+++<wbr>+++**::part(arrow)**`

Tooltip:

Root element:: `vaadin-tooltip-overlay`


=== Parts

Tooltip surface:: `vaadin-tooltip-overlay+++<wbr>+++**::part(overlay)**`
Content wrapper:: `vaadin-tooltip-overlay+++<wbr>+++**::part(content)**`

There are also some in the general component styling docs which needs an update.

[web-padawan]

Thanks, fixed. Also updated general styling docs to not mention date-picker overlay.

[web-padawan]

We might add custom CSS property for this and then list it when adding base styles properties docs.