www/templates/account/plans/includes/billing-address-form.php
<!-- Address form -->
<form class="plan-summary-address" id="plan-summary-address-form">
    <div class="box card-section signup-flow-layout">
        <div class="contents-container">
            <h3>Billing Address</h3>

            <div class="form-input address">
                <label for="street-address">Billing Address</label>
                <input name="street-address" type="text" value="<?= $street_address ?>" required />
            </div>

            <div class="form-input city">
                <label for="city">City</label>
                <input name="city" type="text" value="<?= $city ?>" required />
            </div>
            <div class="form-input state">
                <label for="state">State</label>
                <select autocomplete="off" name="state" data-country-selector="state-selector" required>
                    <?php foreach ($state_list as $state) : ?>
                        <option value="<?= $state['code'] ?>">
                            <?= $state['name']; ?>
                        </option>
                    <?php endforeach; ?>
                </select>
            </div>
            <div class="form-input country">
                <label for="country">Country</label>
                <select autocomplete="off" name="country" data-country-selector="selector" required>
                    <?php foreach ($country_list as $country) : ?>
                        <option value="<?= $country["code"] ?>" <?php ($country["code"] === "US") ? 'selected' : '' ?>>
                            <?= $country["name"]; ?>
                        </option>
                    <?php endforeach; ?>
                </select>
            </div>
            <div class="form-input zip">
                <label for="zipcode">Postal Code</label>
                <input type="text" name="zipcode" value="<?= $zipcode ?>" required />
            </div>

            <input type="hidden" name="type" value="account-signup-preview" />
            <input type="hidden" name="plan" value="<?= $plan->getId() ?>" />
            <input type="hidden" name="csrf_token" value="<?= $csrf_token; ?>" />
            <div class="add-subscription-button-wrapper form-input">
                <button type="submit" class="pill-button yellow"><span data-id="pulse"></span><span data-id="button-text">Add Billing Address</span></button>
            </div>
        </div>
    </div>
</form>

<script defer src="/assets/js/country-list/country-list.js?v=<?= constant('VER_JS_COUNTRY_LIST') ?>"></script>
<script>
    (() => {
        // state dropdown
        const countryList = <?= $country_list_json_blob ?>;
        if (document.readyState === "loading") {
            document.addEventListener("DOMContentLoaded", () => {
                const countrySelectorEl = document.querySelector("[data-country-selector=selector]");
                const divisionSelectorEl = document.querySelector("[data-country-selector=state-selector]");

                new CountrySelector(countrySelectorEl, divisionSelectorEl, countryList);
            });
        } else {
            const countrySelectorEl = document.querySelector("[data-country-selector=selector]");
            const divisionSelectorEl = document.querySelector("[data-country-selector=state-selector]");

            new CountrySelector(countrySelectorEl, divisionSelectorEl, countryList);
        }
    })();
</script>

<script defer src="/assets/js/estimate-taxes.js?v=<?= constant('VER_JS_ESTIMATE_TAXES') ?>"></script>