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.

01-html-structure/04-tables-and-forms/README.md

@@ -0,0 +1,40 @@
+# 练习 4：表格与表单
+
+## 目标
+
+掌握结构化数据和信息收集的 HTML 写法。
+
+## 你要练什么
+
+- `table`
+- `thead`
+- `tbody`
+- `tr`
+- `th`
+- `td`
+- `form`
+- `label`
+- `input`
+- `textarea`
+- `button`
+
+## 任务
+
+请完成一个“前端训练营报名页”，要求包含：
+
+- 一个课程安排表格
+- 表格至少 3 列、3 行数据
+- 一个报名表单
+- 表单中至少有姓名、邮箱、学习目标、提交按钮
+
+## 检查点
+
+- 表头是否使用 `th`
+- 数据是否使用 `td`
+- 表单控件是否和 `label` 对应
+- 提交按钮是否在 `form` 中
+
+## 文件
+
+- [starter.html](/Volumes/Macintosh HD 1/home/front-end-example/01-html-structure/04-tables-and-forms/starter.html)
+- [answer.html](/Volumes/Macintosh HD 1/home/front-end-example/01-html-structure/04-tables-and-forms/answer.html)