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.

README.md

@@ -0,0 +1,39 @@
+# Front-End Study Workspace
+
+这个工作区按知识点分目录，便于你后续继续加入 CSS、JavaScript、DOM、TypeScript 等内容。
+
+## 目录规则
+
+- `01-html-structure`：HTML 结构
+- `02-css-layout`：预留给 CSS
+- `03-javascript-core`：预留给 JavaScript
+- `04-dom-events-async`：预留给 DOM + 事件 + 异步
+- `05-typescript`：预留给 TypeScript
+
+## 当前可学内容
+
+现在已经为你整理好 `01-html-structure`，里面包含：
+
+- 讲义
+- 分阶段练习
+- `starter.html` 起始代码
+- `answer.html` 参考答案
+
+现在也已经整理好 `02-css-layout`，里面包含：
+
+- CSS 讲义
+- 分阶段案例
+- `starter.html` / `starter.css` 起始代码
+- `answer.html` / `answer.css` 参考答案
+
+两部分现在都已经补充到“核心主线 + 常见细分知识点”。
+
+## 使用方式
+
+1. 先阅读 [01-html-structure/README.md](/Volumes/Macintosh HD 1/home/front-end-example/01-html-structure/README.md)
+2. 再阅读 [02-css-layout/README.md](/Volumes/Macintosh HD 1/home/front-end-example/02-css-layout/README.md)
+3. 按顺序完成每个练习目录
+4. 先写 `starter.html` 或 `starter.css`
+5. 写完后再对照答案文件
+
+如果你后面要继续学其他知识点，我可以按同样结构继续给你补 `03-javascript-core`、`04-dom-events-async` 等目录。