Image Cropper: Improve contrast of append label in crop options editor (closes #22878)

[andreaslborg]

Description

Suggestion fix for #22878

The px append label in the image crops property editor (and media picker local crops) was styled using --uui-color-disabled / --uui-color-disabled-contrast, which produced poor contrast between the text and background.

Updated to use --uui-color-surface-alt and --uui-color-text to match the styling used by the UUI library's own input component.

Before:

After:

Dark mode:

Testing

1. Open the Image Cropper property editor
2. Create a crop option under Settings
3. See the contrast in the append

[github-actions]

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[AndyButland]

Looks much better, and improves accessibility. Thanks @andreaslborg.

[AndyButland]

Cherry picked to release/17.5.0 and release/18.0.

[bjarnef]

@AndyButland in addition to this, I wonder if we could have a structure like the following, which makes it simpler to re-use the "addons", without copying the styles and if changes are made later.

It could look similar to this:

<umb-input-group>
	<umb-input-addon slot="prepend">px</umb-input-addon>

	<uui-input
		label="Height"
		id="height"
		name="height"
		type="number"
		autocomplete="false"
		required
		.value=${initial?.height ?? ''}
		min="0">
	</uui-input>

	<umb-input-addon slot="append">px</umb-input-addon>
</umb-input-group>

import { LitElement, css, html } from 'lit';
import { customElement } from 'lit/decorators.js';

@customElement('umb-input-group')
export class UmbInputGroupElement extends LitElement {
	static styles = css`
		:host {
			display: flex;
			align-items: stretch;
		}

		::slotted(uui-input) {
			flex: 1;
		}
	`;

	render() {
		return html`
			<slot name="prepend"></slot>
			<slot></slot>
			<slot name="append"></slot>
		`;
	}
}

import { LitElement, css, html } from 'lit';
import { customElement } from 'lit/decorators.js';

@customElement('umb-input-addon')
export class UmbInputAddonElement extends LitElement {
	static styles = css`
		:host {
			padding-inline: var(--uui-size-space-4);
			background: var(--uui-color-surface-alt);
			border-left: 1px solid var(--uui-color-border);
			color: var(--uui-color-text);
			font-size: var(--uui-type-small-size);
			display: flex;
			align-items: center;
		}
	`;

	render() {
		return html`<slot></slot>`;
	}
}

Some extra which could be added:

:host {
	display: inline-flex;
	align-items: stretch;
}

::slotted(umb-input-addon:first-child) {
	border-radius: 4px 0 0 4px;
}

::slotted(uui-input) {
	border-radius: 0;
}

::slotted(umb-input-addon:last-child) {
	border-radius: 0 4px 4px 0;
}

but it could possible also be part of UI library.

By default there is no standard styling of prepend/append, so up to the developer what they like:
https://uui.umbraco.com/?path=/story/uui-input--prepend-and-append

It would be great if it was easier to inherit the addon styles and just override via CSS variables, e.g. in themes.