feat: Add CSS layout exercises and corresponding HTML files

- Created multiple exercises under the CSS layout section, including:
  - Final page layout with CSS styles and HTML structure.
  - Display and flow concepts with examples of block, inline, and none display types.
  - Selectors and pseudo-classes with practical examples.
  - Overflow and sizing handling in CSS.
  - Grid layout basics for two-dimensional layouts.
  - Fixed and sticky positioning examples.
  - Centering techniques for common layout scenarios.

- Added README files for each exercise to outline objectives and file structures.
- Updated main README to include new sections and usage instructions.

02-css-layout/04-position-badge/README.md

@@ -0,0 +1,29 @@
+# 练习 4：定位与徽标
+
+## 目标
+
+理解 `position: relative` 和 `position: absolute` 的配合。
+
+## 你要练什么
+
+- `position: relative`
+- `position: absolute`
+- `top`
+- `right`
+- `z-index`
+
+## 任务
+
+请完成一个课程推荐卡片，要求：
+
+- 卡片右上角有一个“热门”徽标
+- 徽标固定贴在卡片角上
+- 卡片主体仍保持正常排版
+- 按钮和标题之间留出合理距离
+
+## 文件
+
+- [starter.html](/Volumes/Macintosh HD 1/home/front-end-example/02-css-layout/04-position-badge/starter.html)
+- [starter.css](/Volumes/Macintosh HD 1/home/front-end-example/02-css-layout/04-position-badge/starter.css)
+- [answer.html](/Volumes/Macintosh HD 1/home/front-end-example/02-css-layout/04-position-badge/answer.html)
+- [answer.css](/Volumes/Macintosh HD 1/home/front-end-example/02-css-layout/04-position-badge/answer.css)