For Width="100%" for the textbox, the following can be a workaround:
<style>
.k-floating-label-container {
width: 100%;
}
</style>
<div style="width: 400px; border: 1px solid red;">
<TelerikTextBox Label="the label" Width="100%" @bind-Value="@theValue"></TelerikTextBox>
</div>
@code{
string theValue { get; set; } = "lorem ipsum dolor sit amet";
}
Regards,
Marin Bratanov
Progress Telerik