bug(stepper): bad contrast of step icon in untouched state for M2

[json-derulo]

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

No response

Description

When using a custom theme, in the stepper it can happen that the step icon (step number or state icon) has a bad contrast:

It depends on the contrast color of the primary color. If it's white, everything works correctly, but if it's black, this issue occurs. However for the untouched state, it should always be white, regardless of the contrast color.

Dark mode has the same issue. Here it can even be reproduced in the v16 docs app after selecting the "Purple & Green" theme:

I was not able to reproduce this with M3, the predefined themes work fine. I didn't try custom M3 themes though.

Reproduction

StackBlitz link: https://stackblitz.com/edit/61i1fz?file=src%2Fstyles.scss Steps to reproduce:

1. Configure a primary color with black as a contrast color in light theme, or white as a contrast color in dark theme
2. Use the stepper

Expected Behavior

The step icon has sufficient contrast in untouched state

Actual Behavior

The step icon has insufficient contrast in untouched state

Environment

Angular CLI: 18.0.2 Node: 18.20.3 Package Manager: yarn 1.22.19 OS: linux x64

Angular: 18.0.1 ... animations, common, compiler, compiler-cli, core, forms ... localize, platform-browser, platform-browser-dynamic, router

Package Version

@angular-devkit/architect 0.1800.2 @angular-devkit/build-angular 18.0.2 @angular-devkit/core 18.0.2 @angular-devkit/schematics 18.0.2 @angular/cdk 18.1.2 @angular/cli 18.0.2 @angular/material 18.1.2 @angular/material-experimental 18.1.2 @angular/material-moment-adapter 18.1.2 @schematics/angular 18.0.2 rxjs 7.4.0 typescript 5.4.5 zone.js 0.14.6

[MadunaThabo]

Hello

it would seem that the header-icon-foreground-color is applied from the theme passed through

I would recommend just changing the color of the mat-step-icon in your css

[json-derulo]

Actually it's very easy to fix. Add this to your global styles:

.mat-step-icon {
  --mat-stepper-header-icon-foreground-color: #fff; // or #000 for dark theme
}

The --mat-stepper-header-icon-foreground-color variable just contains the wrong value in M2 themes. It should be hard coded white for light theme, and hard coded black for dark theme.

[andrewseguin]

Agreed that this is not a problem in the actual styles, but an issue with the palette definitions. The contrast colors are likely defined incorrectly