Bootstrap text input length automatically adjust

Bootstrap text input length automatically adjust

How do I set the length of a textbox input When I set it like in ASP.net MVC
<div class="form-group">
@Html.TextBoxFor(m => m.FirstName, new { style = "width:550px",
@class = "form-control" })
</div>
the length is set to 550px, put on mobile display the textbox doesn't
shrink. If I remove the 550px, the text input is 100% long all the way
across the screen and it adjusts on mobile screen.
I want the input at a reasonable length at 550px and I want it to shrink
on a mobile display automatically.
Is there a way to automatically shrink this input box on mobile display in
Twitter Bootstrap?