Added New techstack for CSS

docs/c++/cpp-basics.md

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+// ...existing code...
+# C++ Tech Stack
+
+Brief, practical tech stack and examples for modern C++ projects (aligned with CONTRIBUTING.md style).
+
+## What is this tech stack?
+A curated set of compilers, build tools, libraries, testing and CI tools commonly used for developing reliable, cross-platform C++ applications and libraries.
+
+## Core Components
+
+- Compilers
+  - GCC (g++)
+  - Clang (clang++)
+  - MSVC (cl.exe) — Windows
+- Build systems
+  - CMake (recommended)
+  - Meson, Bazel (alternatives)
+- Package managers
+  - Conan, vcpkg
+- Testing
+  - Catch2, GoogleTest
+- Formatting & linting
+  - clang-format, clang-tidy
+- Debugging & profiling
+  - gdb, lldb, Visual Studio Debugger, valgrind, perf
+- Static analysis
+  - cppcheck, clang-tidy, clang-analyzer
+- CI/CD
+  - GitHub Actions, GitLab CI, Azure Pipelines
+- IDEs & Editors
+  - Visual Studio Code (with C/C++ extension), CLion, Visual Studio, Qt Creator
+
+## Basic Example
+
+Hello world (file: src/main.cpp)
+```cpp
+#include <iostream>
+
+int main() {
+    std::cout << "Hello, C++ tech stack!\n";
+    return 0;
+}
+```
+Expected output:
+```
+Hello, C++ tech stack!
+```
+
+## Minimal CMakeLists.txt
+```cmake
+cmake_minimum_required(VERSION 3.16)
+project(hello_cpp LANGUAGES CXX)
+set(CMAKE_CXX_STANDARD 20)
+add_executable(hello src/main.cpp)
+```
+
+## Example unit test (Catch2)
+```cpp
+// tests/test_example.cpp
+#define CATCH_CONFIG_MAIN
+#include <catch2/catch.hpp>
+
+int add(int a, int b) { return a + b; }
+
+TEST_CASE("addition works") {
+    REQUIRE(add(2,3) == 5);
+}
+```
+
+## CI snippet (GitHub Actions - build & test)
+```yaml
+name: CI
+on: [push, pull_request]
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        compiler: [gcc, clang]
+    steps:
+      - uses: actions/checkout@v4
+      - name: Install dependencies
+        run: sudo apt-get update && sudo apt-get install -y build-essential cmake
+      - name: Configure
+        run: cmake -S . -B build
+      - name: Build
+        run: cmake --build build --config Release
+      - name: Test
+        run: ctest --test-dir build --output-on-failure
+```
+
+## File organization
+```
+project/
+├─ src/
+│  └─ main.cpp
+├─ include/
+│  └─ project/
+├─ tests/
+│  └─ test_example.cpp
+├─ CMakeLists.txt
+└─ .github/workflows/ci.yml
+```
+
+## Common Pitfalls
+- Undefined behavior (use sanitizers: -fsanitize=address,undefined,leak)
+- Mixing ABIs or incompatible compiler flags
+- Missing header guards / pragma once issues
+- Manual memory mistakes — prefer smart pointers and RAII
+
+## Best Practices
+- Use modern C++ (RAII, smart pointers, move semantics, constexpr, spans)
+- Keep headers minimal; prefer pimpl or modules for large projects
+- Enforce style with clang-format and checks in CI
+- Write unit tests and run sanitizers in CI
+- Use CMake modern targets and interface libraries (target_include_directories / target_compile_features)
+
+## Related Topics
+- C++ core guidelines — https://isocpp.github.io/CppCoreGuidelines/CppCoreGuidelines
+- CMake documentation — https://cmake.org/documentation/
+- Conan — https://conan.io
+- Catch2 — https://github.com/catchorg/Catch2
+
+## References
+- cppreference: https://en.cppreference.com
+- Sanitizers & Undefined Behavior: https://clang.llvm.org/docs/UndefinedBehaviorSanitizer.html

docs/c-sharp/c-sharp-basics.md

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+# C# Tech Stack
+
+Brief, practical tech stack and examples for modern C#/.NET projects (aligned with CONTRIBUTING.md style).
+
+## What is this tech stack?
+A concise set of SDKs, frameworks, tools and practices for building cross-platform .NET applications: web, APIs, libraries, and CLI tools.
+
+## Core Components
+- Runtime / SDK
+  - .NET SDK (dotnet 6, 7, 8+)
+- Frameworks
+  - ASP.NET Core, MAUI, Blazor
+- Build & tooling
+  - dotnet CLI, MSBuild
+- Package manager
+  - NuGet
+- Testing
+  - xUnit, NUnit, MSTest
+- Formatting & linting
+  - dotnet format, StyleCop.Analyzers, EditorConfig
+- Debugging & profiling
+  - Visual Studio debugger, dotnet-trace, dotnet-counters, JetBrains dotTrace
+- Static analysis
+  - Roslyn analyzers, SonarQube
+- CI/CD
+  - GitHub Actions, Azure Pipelines, GitLab CI
+- IDEs
+  - Visual Studio, VS Code (C# extension), Rider
+
+## Basic Example
+
+Program.cs
+```csharp
+using System;
+
+class Program {
+    static void Main() {
+        Console.WriteLine("Hello, .NET!");
+    }
+}
+```
+Expected output:
+```
+Hello, .NET!
+```
+
+## Minimal .csproj
+```xml
+<Project Sdk="Microsoft.NET.Sdk">
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+    <TargetFramework>net8.0</TargetFramework>
+  </PropertyGroup>
+</Project>
+```
+
+## Example unit test (xUnit)
+```csharp
+// tests/CalculatorTests.cs
+using Xunit;
+
+public class Calculator {
+    public int Add(int a,int b) => a + b;
+}
+
+public class CalculatorTests {
+    [Fact]
+    public void Add_Works() {
+        var c = new Calculator();
+        Assert.Equal(5, c.Add(2,3));
+    }
+}
+```
+
+## CI snippet (GitHub Actions)
+```yaml
+name: .NET CI
+on: [push, pull_request]
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - uses: actions/setup-dotnet@v3
+        with:
+          dotnet-version: '8.0.x'
+      - run: dotnet restore
+      - run: dotnet build --configuration Release --no-restore
+      - run: dotnet test --no-build --verbosity normal
+```
+
+## File organization
+```
+project/
+├─ src/
+│  └─ ProjectName/
+│     ├─ Program.cs
+│     └─ ProjectName.csproj
+├─ tests/
+│  └─ ProjectName.Tests/
+├─ .github/workflows/
+└─ README.md
+```
+
+## Common Pitfalls
+- Mixing target frameworks or incompatible package versions
+- Ignoring nullable reference warnings
+- Heavy synchronous I/O on ASP.NET threads
+- Leaking DI scopes or disposing shared services
+
+## Best Practices
+- Prefer async/await for I/O
+- Use DI and small services
+- Enable analyzers and treat warnings as errors in CI
+- Pin package versions for libraries
+- Write unit and integration tests; run them in CI
+
+## Related Topics
+- ASP.NET Core Docs — https://learn.microsoft.com/aspnet/core
+- .NET API Browser — https://learn.microsoft.com/dotnet/api
+
+## References
+- https://dotnet.microsoft.com
+- xUnit: https://xunit.net

docs/css/css-basics.md

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+# CSS Tech Stack
+
+Practical CSS toolset and examples for modern styling workflows (aligned with CONTRIBUTING.md style).
+
+## What is this tech stack?
+A set of preprocessors, tooling, linters and frameworks to write maintainable, responsive and performant styles.
+
+## Core Components
+- Languages & extensions
+  - CSS3, Sass/SCSS, Less, PostCSS
+- Utility frameworks
+  - Tailwind CSS (optional)
+- Build & tooling
+  - PostCSS, Autoprefixer, Vite, webpack
+- Linting & formatting
+  - stylelint, Prettier
+- Testing & QA
+  - visual regression (Percy), cross-browser testing, Lighthouse
+- Performance
+  - critical CSS, purgecss / content scanning (Tailwind purge)
+- Debugging
+  - DevTools (Chrome/Firefox), source maps
+- Editors
+  - VS Code (CSS support, emmet)
+
+## Basic Example
+
+styles.css
+```css
+:root {
+  --brand: #0a84ff;
+}
+
+body {
+  font-family: system-ui, -apple-system, "Segoe UI", Roboto, "Helvetica Neue", Arial;
+  margin: 0;
+  color: #111;
+  background: #fff;
+}
+
+.header {
+  background: var(--brand);
+  color: #fff;
+  padding: 1rem;
+}
+```
+Expected: simple page with a blue header styled by .header.
+
+## Example (Sass)
+```scss
+$brand: #0a84ff;
+
+.header {
+  background: $brand;
+  color: #fff;
+  padding: 1rem;
+  @media (min-width: 768px) {
+    padding: 1.5rem;
+  }
+}
+```
+
+## Build snippet (PostCSS + Autoprefixer)
+- Install: npm install postcss postcss-cli autoprefixer
+- Run: npx postcss src/styles.css -o dist/styles.css
+
+## Common Pitfalls
+- Overly specific selectors that hurt reuse
+- Not using CSS variables for theme values
+- Large unused CSS shipped to production
+- Relying on !important to fix specificity issues
+
+## Best Practices
+- Use logical properties and CSS variables
+- Keep small, reusable component styles
+- Run stylelint and Prettier in CI
+- Purge unused CSS in production builds
+- Prefer layout with Flexbox / Grid, avoid heavy nesting
+
+## Related Topics
+- MDN CSS docs — https://developer.mozilla.org/en-US/docs/Web/CSS
+- Tailwind — https://tailwindcss.com
+- stylelint — https://stylelint.io