Terry Hale

You can reduce the padding on the coupon code field. If that’s not enough, you’ll need to also reduce the font size.

.woocommerce-cart table.cart td.actions .coupon #coupon_code.input-text {
  padding: 6px 4px;
  font-size: 18px !important; /* if needed... */

The best no-plugin way to change text is with jQuery (JavaScript). Sometimes it not easy to understand, but it is so much better for your site.
Add this to a code module on your cart page (or if you need to, add it to Theme Options -> Integrations in the head area).

(function($) { $(document).ready(function() {
  $('#coupon_code').attr('placeholder', 'Discount code');
  $('.coupon .button').prop("value", "Apply discount");
  $('.coupon .button').html("Apply discount");
}); })(jQuery);