feat(css): add new term for margin-block property

content/css/concepts/margins/terms/margin-block/margin-block.md

@@ -0,0 +1,73 @@
+---
+Title: 'margin-block'
+Description: 'Sets the margins on the block-start and block-end sides of an element.'
+Subjects:
+  - 'Web Development'
+  - 'Web Design'
+Tags:
+  - 'Box Model'
+  - 'Margin'
+  - 'Positioning'
+CatalogContent:
+  - 'learn-css'
+  - 'paths/front-end-engineer-career-path'
+---
+
+The **`margin-block`** property sets the margins on the block-start and block-end sides of an element, controlling vertical spacing based on the writing mode and text direction.
+
+## Syntax
+
+```pseudo
+margin-block: <value>;
+```
+
+**Parameters:**
+
+- `<value>`: Specifies the margin size for block-start and block-end. Can be a length (`px`, `em`, `rem`), percentage (`%`), `auto`, or global values (`inherit`, `initial`, `unset`, `revert`).
+
+**Return value:**
+
+None. Sets a layout style on the element; it does not return a value.
+
+## Example 1
+
+The following example sets the start and end margin:
+
+```css
+h1 {
+  margin-block: 20px;
+}
+```
+
+This will display:
+
+![margin-block-example-1](https://raw.githubusercontent.com/Codecademy/docs/main/media/margin-block-example-1.png)
+
+## Example 2
+
+The following example sets the start margin to `5%` and end margin `-10px`:
+
+```css
+h1 {
+  margin-block: 5% -10px;
+}
+```
+
+This will display:
+
+![margin-block-example-2](https://raw.githubusercontent.com/Codecademy/docs/main/media/margin-block-example-2.png)
+
+## Example 3
+
+The following example demonstrates block margins in vertical writing mode:
+
+```css
+h1 {
+  margin-block: 10px 20px;
+  writing-mode: vertical-rl; /* block-start is top, block-end is bottom in vertical mode */
+}
+```
+
+This will display:
+
+![margin-block-example-3](https://raw.githubusercontent.com/Codecademy/docs/main/media/margin-block-example-3.png)