.mat-stepper-horizontal-line,
.mat-horizontal-stepper-header::after,
.mat-horizontal-stepper-header::before {
  top: 27px !important;
  border-top-width: 5px !important;
  transition: background-color 0.3s ease, width 0.3s ease;
}
.mat-step-header[ng-reflect-state="done"]::after,
.mat-step-header[ng-reflect-state="done"]+ .mat-step-header[ng-reflect-state="done"]::before {
  background: green !important;
  transition: background-color 0.5s ease, width 0.5s ease; 
}
.mat-step-header[ng-reflect-state="done"] + .mat-stepper-horizontal-line {
  background: green;
  transition: background-color 0.5s ease; 
}
.mat-step-header[ng-reflect-selected="true"]::before,.mat-step-header[ng-reflect-state="done"]::before{
  background: green;
}
Angular 15
Please check this it will help you out