/**
 * Fallback font override metrics for reducing Cumulative Layout Shift (CLS)
 * These values help create fallback fonts that closely match the dimensions
 * of the target Google Font, minimizing layout shift during font loading.
 *
 * Based on Next.js font optimization techniques:
 * https://developer.chrome.com/blog/font-fallbacks/
 */
export interface FallbackFontMetrics {
    fallbackFont: string;
    ascentOverride: string;
    descentOverride: string;
    lineGapOverride: string;
    sizeAdjust: string;
}
/**
 * Get precalculated fallback font metrics for a Google Font family.
 *
 * Note: These metrics are calculated based on the font's characteristics
 * and help create fallback fonts that minimize layout shift.
 *
 * TODO: In the future, we could calculate these dynamically using fontkit
 * instead of relying on precalculated values. This would support all fonts
 * automatically as new fonts are added to Google Fonts.
 *
 * @param fontFamily - The Google Font family name
 * @returns Fallback font metrics or undefined if not available
 */
export declare function getFallbackFontOverrideMetrics(fontFamily: string): FallbackFontMetrics | undefined;
/**
 * Generate CSS for fallback font with override metrics
 * This CSS should be injected alongside the main font declaration
 */
export declare function generateFallbackFontCSS(fontFamily: string, metrics: FallbackFontMetrics): string;
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