/**
 * Inline-style serialisation for HTML email. Email clients do not run the cascade: Gmail strips
 * `<style>`, Outlook resolves no custom property, and only the `style=""` attribute on the
 * painting element is universally honoured.
 */
/** A declaration map. Numbers are emitted verbatim (already-unitless values like `font-weight`). */
export type EmailStyleDeclarations = Record<string, string | number | null | undefined>;
/**
 * Serialise declarations into an inline `style` attribute value.
 *
 * ```ts
 * emailInlineStyle({ width: EMAIL_SHELL.width, backgroundColor: EMAIL_COLORS.surface })
 * // "width:480px;background-color:#fdfdfb"
 * ```
 *
 * `null` / `undefined` values are dropped, so a conditional declaration needs no branch.
 *
 * @throws if a value contains `var()` or `calc()` (neither survives an email client) or a double
 *   quote (it terminates the `style="…"` attribute).
 */
export declare function emailInlineStyle(declarations: EmailStyleDeclarations): string;