How to make corresponding input text within your form?

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HTML5

bootstrap

ASP.NET5

Hi Team

I have a form, but my input text there is no space in between and struggling to get this one to work. See my logic below and help me to improve it better, please mates.

What I have tried:

<form>
    <div class="input-group mb-2">
        <div class="input-group-prepend">

        </div>
        <label for="firstName">Name:</label>
        <div class="input-group col-md-6 col-md-offset-6 col-sm-6 col-xs-6">
            @Html.TextBoxFor(m => m.FirstName, new { @class = "form-control", type = "text", id = "firstname", autofocus = "autofocus", placeholder = "First Name", required = "required" })
            <br />
            @Html.TextBoxFor(m => m.LastName, new { @class = "form-control", type = "text", id = "lastname", autofocus = "autofocus", placeholder = "Last Name", required = "required" })
        </div>
    </div>
</form>