shopify_checkout_reset.css

/*
 * Shopify checkout reset
 */

/* Reset base elements */
body, h1, h2, h3, h4, h5, h6, p, h1 span.subtitle, h3.divider, #welcome, #container, #container.slim, #main, #container.slim #main, #content, #header, #container.slim #header, #header h1,
#info-bar, #footer, .footer p, #container.slim #footer, #overview, #overview h2, #overview a, #products, #done, #wallet, div.wallet-highlight, #cost, #order-num, #success, #steps, #thumbs,
#thumbs div, #thumbs td, .slim #thumbs td, #thumbs h3, #thumbs h3 span, #thumbs span, #overview .hint, #payment-type, #payment-type li, #payment-type li:hover, li.text-payment, .center,
#addresses, #email, #email label, #email input, #shipping-same label, .address-notification, #gateway-logos, #gateway-logos img, #pay-with, #pay-with h3, #payment, #or, #payment-methods li,
#payment-methods input, #credit-card-valid, img.credit-card, .field-with-errors, .field-with-errors input, .field-with-errors .error-message, .severe-error, .gleft, .gright, label,
input[type=text], input[type=password], textarea, #buttons, #buttons input, dl, dt, dd, dl .hint, .group, .pgroup, .pgroup dl, input.btn, textarea.short, input.digit-2, textarea.tall,
.ta-success, .big, input.long, input.short, .small, label.inline, .pageform h4, .soft, .soft label, .medium label, .medium p, ul.radios li, fieldset, fieldset#switchsolo, legend, fieldset p,
span.hint a, td.label, td.lprice, td.sprice, td.weight, th.trash, th.sku, a.bottab, a.more, a.less, .group h3, .pgroup h3, .form td, .form ul.inline li, .form ul.inline li label, .form td.lbl,
.form td input, .form td input.short, .form td textarea, .highlight, #customer_login.required, .sign-in, .forgot-password, #reset-email, .multiple_address_selection td, table.form.full,
.form.full td.lbl, .form.full td input, .sign-in-area, .sign-in-area input[type=submit], .group.st, h4.active-customer, span.sign-in-message, .flash, .flash.notice, .flash.error,
.header-description p, .thumblist li, .thumblist li:last-child, .thumblist-image, .thumblist-image .images, .thumblist-content, .thumblist .group, .item-inventory-message,
.item-inventory-action, .item-inventory-action label, .item-inventory-action input[type=radio], .shopify-dialog-content, .shopify-dialog pre, .shopify-dialog-content{
  font-family: sans-serif;
  font-size: 100%;
  line-height: 140%;
  font-weight: normal;
  font-style: normal;
  text-align: left;
  vertical-align: baseline;
  color: #000;
  text-shadow: none;
  list-style: none;
  width: auto;
  height: auto;
  margin: 0;
  padding: 0;
  border: none;
  background: transparent;
}

li.text-payment{
  margin: 0 !important; /* li.text-payment uses !important */
}

input, #email input, #payment-methods input, .field-with-errors input, input[type=text], input[type=password], textarea, #buttons input, textarea.short, input.digit-2, textarea.tall, input.long,
input.short, .form td input, .form td input.short, .form td textarea, .form.full td input, .sign-in-area input[type=submit], .item-inventory-action input[type=radio]{
  line-height: 100%;
  border: #ccc solid 1px;
}

#buttons input, .sign-in-area input[type=submit]{
  background: #ddd;
  padding: 5px;
}

/* Reset floats */
#products, #done, #thumbs div, .gleft, .form ul.inline li, .sign-in, .forgot-password, .sign-in-area input[type=submit], .thumblist-image, .thumblist-content{
  float: none;
}

/* Reset absolute or fixed positions */
#info-bar, #payment, #or{
  position: static;
  top: auto;
  right: auto;
  bottom: auto;
  left: auto;
}

/* Reset links */
a{
  color: #479ccf;
}

a:hover{
  color: #2a74a0;
  text-decoration: underline;
}

/* Reset opacity */
.inactive{
  -moz-opacity: 1;
  opacity: 1;
  filter: alpha(opacity=100);
}

Digging your tweaks so I have updated mine with them as well.