Checkout Form Width

Hello,

Can you share the page URL so I can further check on your site and give you a possible CSS code.

Best Regards

Hello,

Please use the below custom CSS code and paste it to Theme Settings > Custom CSS > Mobile CSS section:

/* reset default behavior */
    .woocommerce-checkout .woocommerce-billing-fields .form-row {
        flex: 0 0 100% !important;
        max-width: 100% !important;
    }

    /* First name + Last name */
    .woocommerce-checkout #billing_first_name_field,
    .woocommerce-checkout #billing_last_name_field {
        flex: 0 0 48% !important;
        max-width: 48% !important;
    }

    /* Postcode + State */
    .woocommerce-checkout #billing_postcode_field,
    .woocommerce-checkout #billing_state_field {
        flex: 0 0 48% !important;
        max-width: 48% !important;
    }

    /* wrapper must stay flex */
    .woocommerce-checkout .woocommerce-billing-fields__field-wrapper {
        display: flex !important;
        flex-wrap: wrap !important;
        gap: 10px;
    }

Best Regards.