Green box around radiobuttonlist without validator

Why if I click on radiobuttons of a RadioButtonList, that DOESN'T have any RequiredValidator, it will be drawn a green border around it ?


<RadzenTemplateForm TItem="InputModel" Data=@Model Submit=@Search>

        <div class="row mb-2">
            <div class="col-md-1">
                <RadzenLabel Component="Company" Text="Società" />
            <div class="col-md-11">
                <RadzenRadioButtonList @bind-Value="Model.CompanyId">
                        <RadzenRadioButtonListItem Text="Mic" Value="@("MIC")"></RadzenRadioButtonListItem>
                        <RadzenRadioButtonListItem Text="Mpd" Value="@("MPD")"></RadzenRadioButtonListItem>

This is how Blazor's built-in validation works: it applies the valid CSS class by default. And in the default template the valid class adds a green border. The valid class is defined in the site.css file.