<TelerikFloatingLabel Text="Floating Label Over Mask">
    <TelerikMaskedTextBox @bind-Value="@MaskedValue"
                          Mask="000-000"
                          Width="200px"
                          Class="mask-with-label" />
</TelerikFloatingLabel>

@if (string.IsNullOrEmpty(MaskedValue))
{
    <style>
        .mask-with-label input:not(:focus) {
            color: transparent;
        }
    </style>
}

@code {
    private string MaskedValue { get; set; } = string.Empty;
}