Form Variant

<form action="#">
    <div class="form-btn-inner border rounded-pill">
        <input class="form-control" type="search" placeholder="Search..." />
        <button class="btn btn-primary text-white text-uppercase fw-semiBold py-12 px-20 px-lg-34 shadow-none" type="submit">Send</button>
    </div>
</form>

Variables

You can found SASS Variable on scss/components/bootstrap/forms/_form-variant.scss

Button Inner

$form-btn-inner-background: $white;
$form-btn-inner-padding: 7px;

$form-btn-inner-input-padding-y: 0;
$form-btn-inner-input-padding-x: 20px;