According to your codes and result image, I guess you don’t import the bootstrap or jquery successfully. So the bootstarp class is not work well for your html codes.

I suggest you should firstly include the bootstarp CSS and JavaScript in your razor page and add justify-content-center to the row, then you could find all your control will become center.

Reference:

<!-- Latest compiled and minified CSS -->
<link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/3.4.1/css/bootstrap.min.css">

<!-- jQuery library -->
<script src="https://ajax.googleapis.com/ajax/libs/jquery/3.5.1/jquery.min.js"></script>

<!-- Latest compiled JavaScript -->
<script src="https://maxcdn.bootstrapcdn.com/bootstrap/3.4.1/js/bootstrap.min.js"></script>

Html codes:

<div class="container align-content-center" style="border:solid">
    <div class="row justify-content-center">
        <div class="col-md-6 col-md-offset-3 text-center">
            <div class="form-group">
                <label asp-for="Customer.name">Name:</label>
                <input asp-for="Customer.name" class="form-control text-center" type="text" />
            </div>
            <div class="form-group">
                <label asp-for="Customer.notes">Notes:</label>
                <input asp-for="Customer.notes" class="form-control text-center" />
            </div>
            <div class="form-group">
                <input type="submit" value="Create" class="btn btn-dark text-center" />
            </div>
        </div>
    </div>
</div>

Result:

If you want the lable and the input should in same row, you should modify the html codes to let one form control inside one row like below:

<div class="container" style="border:solid">
    <div class="form-horizontal col-md-offset-3 justify-content-center">
        <div class="form-group ">
            <label asp-for="Customer.name" class=" col-md-2 control-label">Name:</label>
            <div class="col-md-4">
                <input asp-for="Customer.name" class="form-control text-center" type="text" />
            </div>
        </div>
        <div class="form-group ">

            <label asp-for="Customer.notes" class=" col-md-2 control-label">notes:</label>
            <div class="col-md-4">
                <input asp-for="Customer.notes" class="form-control text-center" type="text" />
            </div>
        </div>
        <div class="form-group ">
            <div class="col-md-6 text-center">
                <input type="submit" value="Create" class="btn btn-dark text-center" />
                </div>
            </div>
        </div>
</div>

Result:

I can’t seem to figure out how to center some input boxes inside my ASP.NET Core web application. I have been trying out CSS solutions and using different HTML solutions like class = “text-center”, but I haven’t gotten any results yet. Here is the code that I have at the moment trying to center these boxes on the page:

@page
@model CustomerPageTest.Pages.Customer.AddCustomerModel

@{
    ViewData["Title"] = "AddCustomer";
}

@{ 
    Layout = null; //Added
}

<div class="container align-content-center" style="border:solid">
    <div class="row">
        <div class="col-md-6 col-md-offset-3 text-center">
            <div class="form-group">
                <label asp-for="Customer.name">Name:</label>
                <input asp-for="Customer.name" class="form-control text-center" type="text" />
            </div>
            <div class="form-group">
                <label asp-for="Customer.notes">Notes:</label>
                <input asp-for="Customer.notes" class="form-control text-center" />
            </div>
            <div class="form-group">
                <input type="submit" value="Create" class="btn btn-dark text-center" />
            </div>
        </div>
    </div>
</div>

This is the result I get when I run the application:

Sorry for the size of it, I’m not sure how to enlarge that. Either way, everything stays on the left. Is there some type of bootstrap file I should be importing to fix this?