make bootstrap buttons thinner code example

Example: button with sign in image bootstrap 4

<link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/4.0.0/css/bootstrap.min.css" integrity="sha384-Gn5384xqQ1aoWXA+058RXPxPg6fy4IWvTNh0E263XmFcJlSAwiGgFAW/dAiS6JXm" crossorigin="anonymous">

<p class="mb-0">px-3:</p>
<a class="btn btn-lg px-3 btn-primary" href="#" role="button">USA <img src="https://lipis.github.io/flag-icon-css/flags/4x3/in.svg" height="30" alt="USA flag"></a>
<p class="mb-0">px-4:</p>
<a class="btn btn-lg px-4 btn-primary" href="#" role="button">USA <img src="https://lipis.github.io/flag-icon-css/flags/4x3/in.svg" height="30" alt="USA flag"></a>
<p class="mb-0">px-5:</p>
<a class="btn btn-lg px-5 btn-primary" href="#" role="button">USA <img src="https://lipis.github.io/flag-icon-css/flags/4x3/in.svg" height="30" alt="USA flag"></a>