I have been trying to center a div for hours and nothing seems to work. I have tried margin: auto, flexbox, and grid. What is the definitive way to center a div both horizontally and vertically?

I am new to JavaScript and I keep seeing `let`, `const`, and `var` used for variable declarations. What are the key differences between them, and when should I use each?

I want to start a new Next.js project and I prefer using TypeScript. What is the recommended way to initialize a Next.js project with TypeScript support?