I have found a solution.

When making any change to the .less files within your custom theme, follow the following four steps.

1. Delete the files within: <vendor>\var\view_preprocessed\pub\static\frontend\<vendor_theme>\en_NZ\css
2. Delete the files within: <vendor>\var\cache
3. Delete the files within: <vendor>\pub\static\frontend\<vendor_theme_name>\en_NZ\css
4. If in production mode, run the setup:di:compile command. If in developer mode, simply refresh the page you are attempting to style.

After following these steps, I was able to observe the changes I made to my website.

I have found a solution.

When making any change to the .less files within your custom theme, follow the following four steps.

1. Delete the files within: <vendor>\var\view_preprocessed\pub\static\frontend\<vendor_theme>\en_NZ\css
2. Delete the files within: <vendor>\var\cache
3. Delete the files within: <vendor>\pub\static\frontend\<vendor_theme_name>\en_NZ\css
4. If in production mode, run the setup:static-content:deploy command. If in developer mode, simply refresh the page you are attempting to style.

After following these steps, I was able to observe the changes I made to my website.