What is the @font-face rule, and how is it used to import custom fonts?

The `@font-face` rule is a CSS at-rule used to define custom font families and specify the sources from which the font files should be loaded. It allows web developers to use custom fonts in their web pages by providing instructions to the browser on how to download and render the fonts. Here's how the `@font-face` rule is used to import custom fonts:

1. **Define Font Family**:
   - Start by defining a custom font family name using the `font-family` property. This name will be used to reference the custom font throughout the CSS stylesheets.

   ```css
   @font-face {
       font-family: 'CustomFont';
   }
   ```

2. **Specify Font Sources**:
   - Specify the sources from which the font files should be loaded using the `src` property. You can provide multiple font file formats to ensure cross-browser compatibility.

   ```css
   @font-face {
       font-family: 'CustomFont';
       src: url('path/to/font.woff2') format('woff2'), /* Modern browsers */
            url('path/to/font.woff') format('woff');   /* Legacy browsers */
   }
   ```

3. **Optional: Specify Font Characteristics**:
   - Optionally, you can specify additional font characteristics such as font weight, font style, and font display behavior using properties like `font-weight`, `font-style`, and `font-display`.

   ```css
   @font-face {
       font-family: 'CustomFont';
       src: url('path/to/font.woff2') format('woff2'),
            url('path/to/font.woff') format('woff');
       font-weight: normal; /* or bold, 400, 700, etc. */
       font-style: normal;  /* or italic */
       font-display: swap;  /* or fallback, optional */
   }
   ```

4. **Apply Font to Elements**:
   - Once the `@font-face` rule is defined, you can apply the custom font to specific HTML elements using the `font-family` property in your CSS stylesheets.

   ```css
   body {
       font-family: 'CustomFont', sans-serif; /* Apply custom font with fallback */
   }
   ```

By using the `@font-face` rule, you can import custom fonts into your web pages and use them to style text content. This allows you to achieve a unique typographic design and enhance the visual appeal of your website. Additionally, specifying font file formats and font characteristics ensures compatibility with different browsers and devices, providing a consistent experience for users across various platforms.