how can i override simple_form bootstrap style with my bootstrap form styles

i have built simple_form fields in my railsapp,when i adding simple_form tag it style get changes, and i want to integrate this simple_form with my alredy built frontend bootstrap forms this is my

bootstrap form

<input type="text" class="form-control" placeholder="Username" required autofocus />

simple_form filed

<%= f.input :email,html:{class: "form-control"},required: false,autofocus: true %>