Bulma class: .is-expanded

    <div class="field has-addons">
        <p class="control">
            <input class="input" type="text" placeholder="Example text">
        </p>
        <p class="control">
            <a class="button">
                Button
            </a>
        </p>
    </div>
    <div class="field has-addons">
        <p class="control is-expanded">
            <input class="input" type="text" placeholder="Text in expanded element">
        </p>
        <p class="control">
            <a href="#" class="button">
                Button
            </a>
        </p>
    </div>