Zend certified PHP/Magento developer

How to access global variables in a custom less file

Using Magento 2.3.4

I have a Custom Layout Update set for one of my CMS Pages, in this layout update I reference custom.css which has a corresponding custom.less. If I don’t use global variables I can change the styling without issues, but I lack access to project-wide variables. I plan to control the styles of multiple pages through this file, so being able to access globals would be a big help.

I placed custom.less in the following directory VENDOR/CUSTOM_THEME/Magento_Cms/web/css.

Currently, I get this error:

[2020-05-11 19:28:00] main.CRITICAL: variable @media-common is undefined in file /var/www/html/var/view_preprocessed/pub/static/frontend/VENDOR/THEME/en_US/Magento_Cms/css/custom.less in custom.less on line 10, column 9
08| //  Common
09| //  _____________________________________________

How can I access things like media queries and variables for fonts in custom.less?