How do you handle font loading fallbacks in case the custom font fails to load?

Handling font loading fallbacks is essential to ensure that text remains readable and accessible if the custom font fails to load or is unavailable. Here's how you can handle font loading fallbacks effectively:

1. **Specify Fallback Font Families**:
   - Include fallback font families in your CSS declarations to provide alternatives in case the custom font fails to load. Use generic font families like `sans-serif`, `serif`, or `monospace` as fallbacks to ensure broad compatibility across different platforms and devices.

   ```css
   body {
       font-family: 'CustomFont', sans-serif; /* Fallback to sans-serif */
   }
   ```

2. **Use System Fonts as Fallbacks**:
   - Consider using system fonts as fallbacks, especially for critical text content like headings and body text. System fonts are pre-installed on users' devices and offer reliable fallback options in case the custom font fails to load.

   ```css
   h1 {
       font-family: 'CustomFont', -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, Oxygen, Ubuntu, Cantarell, 'Open Sans', 'Helvetica Neue', sans-serif; /* Fallback to system fonts */
   }
   ```

3. **Progressive Enhancement**:
   - Implement progressive enhancement by loading the custom font asynchronously and applying it only after it has successfully loaded. In the meantime, display text using fallback font families to ensure immediate readability.

   ```html
   <link rel="stylesheet" href="custom-font.css" media="print" onload="this.media='all'">
   ```

4. **Font Loading API**:
   - Use the Font Loading API to detect when the custom font has finished loading and apply it dynamically to text elements. In the meantime, use fallback font families to display text content.

   ```javascript
   var font = new FontFace('CustomFont', 'url(path/to/custom-font.woff2)');
   font.load().then(function() {
       document.fonts.add(font);
       document.body.style.fontFamily = 'CustomFont, sans-serif';
   }).catch(function() {
       document.body.style.fontFamily = 'sans-serif';
   });
   ```

5. **Font Display Descriptors**:
   - Use font-display descriptors in your @font-face rules to control how fonts are displayed while loading. Options like `swap`, `fallback`, and `optional` allow you to specify fallback behavior in case the custom font fails to load.

   ```css
   @font-face {
       font-family: 'CustomFont';
       src: url('path/to/custom-font.woff2') format('woff2');
       font-display: swap; /* Fallback to system font until custom font loads */
   }
   ```

By implementing these strategies, you can ensure that text remains readable and accessible even if the custom font fails to load, providing a seamless user experience across different browsers and devices.