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/05-final-page/starter.css

@@ -0,0 +1,34 @@
+body {
+}
+
+.page {
+}
+
+.site-header {
+}
+
+.nav {
+}
+
+.hero {
+}
+
+.hero-link {
+}
+
+.tracks {
+}
+
+.track-card {
+}
+
+.contact {
+}
+
+.form {
+}
+
+input,
+textarea,
+button {
+}