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/answer.css

@@ -0,0 +1,38 @@
+body {
+  margin: 0;
+  min-height: 100vh;
+  display: grid;
+  place-items: center;
+  background: #fff7ed;
+  font-family: "PingFang SC", "Microsoft YaHei", sans-serif;
+}
+
+.card {
+  position: relative;
+  width: 360px;
+  padding: 32px 24px 24px;
+  border-radius: 20px;
+  background: #ffffff;
+  border: 1px solid #fed7aa;
+  box-shadow: 0 18px 40px rgba(234, 88, 12, 0.12);
+}
+
+.badge {
+  position: absolute;
+  top: -10px;
+  right: 18px;
+  z-index: 1;
+  padding: 6px 12px;
+  border-radius: 999px;
+  background: #ea580c;
+  color: #ffffff;
+  font-size: 14px;
+}
+
+a {
+  display: inline-block;
+  margin-top: 18px;
+  color: #9a3412;
+  text-decoration: none;
+  font-weight: 700;
+}