Drupal 8 hook_menu() to render hook_theme()

I am finally diving in to Drupal 8 for a project. In my module though I can not seem to nail down how to render a template from my module based on the route.

In Drupal 7 I would normally do this

custom.module

function union_views_menu() {
    $items = array();

    $items['home'] = array(
        'title' => 'Home',
        'description' => 'home apge',
        'page callback' => 'home_page',
        'access arguments' => array( 'access content'),
        'type' => MENU_CALLBACK
    );
    return $items;
}

function home_page() {
    return theme('home_page');
}

function union_views_theme(){
    return array(
        'home_page'     => array(
            'template'  => 'templates/home-page'
        )
  );
}

And then I would have a template in the templates folder

With Drupal 8 I got to about here:

custom.routing.yml

custom:
    path: /home
    defaults: 
        _controller: Drupal\custom\Controller\CustomController::custom
    requirements:
        _permission: 'access content'

src/Controller/CustomController.php

namespace Drupal\custom\Controller;

class CustomController {
    public function custom(){
        return array(
            '#title' => 'Custom Theme',
            '#markup' => 'This is a content.'
        );
    }
}

And all the works great for getting to the route. But I can not seem to figure out creating a hook_theme function for my hook_menu to use as a callback.

Figured it out

Add custom.module

function custom_theme() {
    $theme['home_page'] = [
        'variables' => ['name' => NULL],
        'template' => 'home_page'
    ];

    return $theme;
}

in my controller replaced '#markup' with:

'#theme' => 'home_page'