Bootstrap classes in Visual studio and creating a webform with bootstrap asp.net visual studio built in web template

 >Go to https://www.w3schools.com/ and see the buttons or textbox classes.

>or go to https://getbootstrap.com/docs/5.1/components/buttons/

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Also you have to add below code, if you are using bootstrap template website or webapp

<%@ Page Title="Home Page" Language="C#" MasterPageFile="~/Site.Master" AutoEventWireup="true" CodeFile="Default.aspx.cs" Inherits="_Default" %>

<asp:Content ID="BodyContent" ContentPlaceHolderID="MainContent" runat="server">

<div>

--------your code here---------change code file and inherits properties of above

</div>

</asp:Content>

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or you can create web form by selecting the checkbox of "select master page"(below is screenshot)