## insertCss · function

Inserts CSS rules into the document, scoping them with a unique class name.

The `style` parameter can be either:
- A **concise style string** (for rules applying to the root class).
- An **object** where keys are selectors (with `&` representing the root class) 
  and values are concise style strings or nested objects. When the key does not contain `&`,
  it is treated as a descendant selector. So `{p: "color:red"}` becomes `".AbdStlX p { color: red; }"` with `AbdStlX` being the generated class name.

### Concise Style Strings

Concise style strings use two syntaxes (same as inline CSS in | A):
- **Short form** `key:value` (no space after colon): The value ends at the next whitespace.
  Example: `'m:$3 bg:red r:8px'`
- **Long form** `key: value;` (space after colon): The value continues until a semicolon.
  Example: `'box-shadow: 2px 0 6px black; transition: all 0.3s ease;'`

Both forms can be mixed: `'m:$3 box-shadow: 0 2px 4px rgba(0,0,0,0.2); bg:$cardBg'`

Supports the same CSS shortcuts as | A and CSS variable references with `$` (e.g., `$primary`, `$3`).

CSS is inserted into the <head> in an order relative to other insert(Global)Css items that is consistent
based on when the containing Aberdeen scope was first defined. This allows changing styles without changing
order-based precedence.

**Signature:** `(style: string | object) => string`

**Parameters:**

- `style: string | object` - - A concise style string or a style object.

**Returns:** The unique class name prefix used for scoping (e.g., `.AbdStl1`). 
Use this prefix with | A to apply the styles.

**Examples:**

Basic Usage with Shortcuts and CSS Variables
```typescript
const cardClass = A.insertCss({
'&': 'bg:white p:$4 r:8px transition: background-color 0.3s;',
'&:hover': 'bg:#f5f5f5',
});

A('section', cardClass, () => { 
A('p#Card content'); 
});
```

Nested Selectors and Media Queries
```typescript
const formClass = A.insertCss({
'&': 'bg:#0004 p:$3 r:$2',
button: {
'&': 'bg:$primary fg:white p:$2 r:4px cursor:pointer',
'&:hover': 'bg:$primaryHover',
'&:disabled': 'bg:#ccc cursor:not-allowed',
'.icon': 'display:inline-block mr:$1',
'@media (max-width: 600px)': 'p:$1 font-size:14px'
}
});

A('form', formClass, () => {
A('button', () => {
A('span.icon text=🔥');
A('#Click Me');
});
});
```

Complex CSS Values
```typescript
const badge = A.insertCss({
'&::before': 'content: "★"; color:gold mr:$1',
'&': 'position:relative box-shadow: 0 2px 8px rgba(0,0,0,0.15);'
});

A(badge + ' span#Product Name');
```
