Utilizing design tokens is key to customizing the css for FluentUI components. I came across a variable in the css named --neutral-stroke-strong-rest and found guidance in the documentation here.
To make this work, following all the setup steps outlined in the documentation is necessary. Then, in your razor page, include your component with a reference to the .cs code:
<FluentProgress @ref="ref1"></FluentProgress>
In the .cs code, it was essential to incorporate:
[Inject]
private NeutralStrokeStrongRest neutralStrokeStrongRest { get; set; } = default!;
private FluentProgress? ref1;
Additionally, adding a function to modify the CSS variables using JS was required (further details in the docs):
protected override async Task OnAfterRenderAsync(bool firstRender)
{
if (firstRender)
{
await neutralStrokeStrongRest.SetValueFor(ref1.Element, "#FFFFFF".ToSwatch());
StateHasChanged();
}
}
And just like that, the progress bar no longer displays a track!