bug(theming): Custom theme created using ng-add reduces overall font-size #31611

Is this a regression?

• Yes, this behavior used to work in the previous version

The previous version in which this bug was not present was

Not sure exactly, but 20.1.0

Description

With version 20.1.1, ng-add commands add below line in scss file, which causes overall font-sizes to be reduced.

font: var(--mat-sys-body-medium);

I think this go introduced with #31522

Reproduction

StackBlitz link: https://stackblitz.com/edit/4fzceyzs?file=src%2Fstyles.scss
Steps to reproduce:

1. Observe the buttons' font-sizes, it's not same as what is given in docsite example https://material.angular.dev/components/button/overview#button-overview
2. Comment the line font: var(--mat-sys-body-medium); to see that font-sizes are back to normal

Expected Behavior

Font-size should be same as what is given in docsite when we run ng-add.

Actual Behavior

Font-sizes are not same as what is given in docsite when we run ng-add.

Environment

• Angular: 20.1.0
• CDK/Material: 20.1.3 (on stackblitz it's 20.1.0, but the content of styles.scss is same as the content of file which is generated using 20.1.3)
• Browser(s): Chrome
• Operating System (e.g. Windows, macOS, Ubuntu): macOS