V8: Style the umb-overlay header and footer like the rest of the overlays

[kjac]

Prerequisites

• I have added steps to test this contribution in the description below

Description

The header and footer of the umb-overlay dialog look rather out of place when the dialog is used in "slide-in-from-right" mode; I think they may be leftovers from V7.

Here's a V8 style dialog:

...and here are a few select samples of umb-overlay:

Notice:

• The height of the header and footer (and how they do not align nicely with the main window header and footer)
• The font size of the header
• The border color that separates the dialog content from the header and footer
• The background color of the footer
• The lack of padding in the top of the dialog content
• The white border near the footer when the dialog has a scrollbar

This PR updates the styling of umb-overlay so it looks like a V8 dialog in "slide-in-from-right" mode:

The styling of umb-overlay when used e.g. for picking items types in Grid or Nested Content remains (largely) unchanged:

Testing this PR

Verify that the umb-overlay look and feel is V8-ish 😄

At the time of writing, umb-overlay is used for:

• Edit dialog when inserting or editing images from RTE
• User profile dialog when clicking the user avatar in the upper left corner
• File type picker when uploading new images via the dropzone (provided you have multiple "image" media types)
• Fields list per search result in the Examine Management dashboard
• New item type picker in the Grid
• New item type picker in Nested Content
• List view YSOD details dialog (I'm not entirely sure how to test this one...)

[emmaburstow]

This is just right. Ok, so we'll check it over and merge if it's all good.

Em

[poornimanayar]

Hey @kjac ,

Tested and great attempt at bringing consistency!

Poornima

[nul800sebastiaan]

It's looks gr8 to me! 👍