Hey guys, I hope all is well. I'm currently attempting to learn more about Auto Layout and constraints programmatically, however I'm having a hard time understanding everything. Basically, I just want to create a small blue view as a subview in my main view, however as I increase the screen size (by selecting different device simulators), my blue rectangle gets bigger, and never stays the same size across device simulators. I thought with constraints and auto layout, the views would appear the same across devices?

Here's the below code that I'm working with:

mainView = UIView()

mainView.backgroundColor = UIColor.blue

view.addSubview(mainView)

mainView.translatesAutoresizingMaskIntoConstraints = false

    NSLayoutConstraint.activate([
        mainView.topAnchor.constraint(equalTo: view.topAnchor, constant: 350),
        mainView.bottomAnchor.constraint(equalTo: view.bottomAnchor, constant: -350),
        mainView.leadingAnchor.constraint(equalTo: view.leadingAnchor, constant: 150),
        mainView.trailingAnchor.constraint(equalTo: view.trailingAnchor, constant: -150)
        ])

I feel like I'm not grasping the concept of Auto Layout and constraints, and how to effectively use them.

Can you guys help point me in the right direction?