https://github.com/toland/qlmarkdown/pull/78

qlmarkdown.css

/* Extracted from github.com */

body {
  -ms-text-size-adjust: 100%;
  -webkit-text-size-adjust: 100%;
  line-height: 1.5;
  color: #b8bfc6;
  /* font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif, "Apple Color Emoji", "Segoe UI Emoji", "Segoe UI Symbol"; */
  font-style: normal;
  line-height: 1.625rem;
  font-family: "Helvetica Neue", Helvetica, Arial, sans-serif;
  font-size: 16px;
  line-height: 1.5;
  word-wrap: break-word;
  padding: 3rem 3rem 8rem 3rem;
  background: #363B40;
}

body a {
  background-color: transparent;
  -webkit-text-decoration-skip: objects;
}

body a:active,
body a:hover {
  outline-width: 0;
}

body strong {
  font-weight: inherit;
}

body strong {
  font-weight: bolder;
}

body h1 {
  font-size: 2em;
  margin: 0.67em 0;
}

body img {
  border-style: none;
}

body svg:not(:root) {
  overflow: hidden;
}

body code,
body kbd,
body pre {
  font-family: monospace, monospace;
  font-size: 1em;
}

body hr {
  box-sizing: content-box;
  height: 0;
  overflow: visible;
}

body input {
  font: inherit;
  margin: 0;
}

body input {
  overflow: visible;
}

body [type="checkbox"] {
  box-sizing: border-box;
  padding: 0;
}

body * {
  box-sizing: border-box;
}

body input {
  font-family: inherit;
  font-size: inherit;
  line-height: inherit;
}

body a {
  color: #e0e0e0;
  text-decoration: none;
}

body a:hover,
body a:active {
  color: #fff;
  text-decoration: underline;
}

body strong {
  font-weight: 600;
}

body hr {
  height: 0;
  margin: 15px 0;
  overflow: hidden;
  background: transparent;
  border: 0;
  border-bottom: 1px solid #474d54;
}

body hr::before {
  display: table;
  content: "";
}

body hr::after {
  display: table;
  clear: both;
  content: "";
}

body table {
  border-spacing: 0;
  border-collapse: collapse;
}

body td,
body th {
  padding: 0;
}

body h1,
body h2,
body h3,
body h4,
body h5,
body h6 {
  margin-top: 0;
  margin-bottom: 0;
}

body h1 {
  font-size: 32px;
  font-weight: 600;
}

body h2 {
  font-size: 24px;
  font-weight: 600;
}

body h3 {
  font-size: 20px;
  font-weight: 600;
}

body h4 {
  font-size: 16px;
  font-weight: 600;
}

body h5 {
  font-size: 14px;
  font-weight: 600;
}

body h6 {
  font-size: 12px;
  font-weight: 600;
}

body p {
  margin-top: 0;
  margin-bottom: 10px;
}

body blockquote {
  margin: 0;
}

body ul,
body ol {
  padding-left: 0;
  margin-top: 0;
  margin-bottom: 0;
}

body ol ol,
body ul ol {
  list-style-type: lower-roman;
}

body ul ul ol,
body ul ol ol,
body ol ul ol,
body ol ol ol {
  list-style-type: lower-alpha;
}

body dd {
  margin-left: 0;
}

body code {
  /* font-family: Consolas, "Liberation Mono", Menlo, Courier, monospace;
  font-size: 12px; */
  font-size: 0.875rem;
  font-family: Monaco, Consolas, "Andale Mono", "DejaVu Sans Mono", monospace;
}

body pre {
  margin-top: 0;
  margin-bottom: 0;
  /* font: 12px Consolas, "Liberation Mono", Menlo, Courier, monospace; */
  font-size: 0.875rem;
  font-family: Monaco, Consolas, "Andale Mono", "DejaVu Sans Mono", monospace;
}

body input {
  -webkit-font-feature-settings: "liga" 0;
  font-feature-settings: "liga" 0;
}

body::before {
  display: table;
  content: "";
}

body::after {
  display: table;
  clear: both;
  content: "";
}

body>*:first-child {
  margin-top: 0 !important;
}

body>*:last-child {
  margin-bottom: 0 !important;
}

body a:not([href]) {
  color: inherit;
  text-decoration: none;
}

body p,
body blockquote,
body ul,
body ol,
body dl,
body table,
body pre {
  margin-top: 0;
  margin-bottom: 16px;
}

body hr {
  height: 0.25em;
  padding: 0;
  margin: 24px 0;
  background-color: #474d54;
  border: 0;
}

body blockquote {
  padding: 0 1em;
  color: #9DA2A6;
  border-left: 0.25em solid #474d54;
}

body blockquote>:first-child {
  margin-top: 0;
}

body blockquote>:last-child {
  margin-bottom: 0;
}

body kbd {
  display: inline-block;
  padding: 3px 5px;
  font-size: 11px;
  line-height: 10px;
  vertical-align: middle;
  color: #fff;
  background-color: #333;
  /* border: solid 1px #ccc;
  border-bottom-color: #bbb; */
  border-radius: 3px;
  box-shadow: inset 0 -1px 0 rgba(0,0,0,.25);
}

body h1,
body h2,
body h3,
body h4,
body h5,
body h6 {
  margin-top: 24px;
  margin-bottom: 16px;
  font-weight: 600;
  line-height: 1.25;
  color: #DEDEDE;
  font-family: "Lucida Grande", "Corbel", sans-serif;
}

body h1 {
  padding-bottom: 0.3em;
  font-size: 2em;
  border-bottom: 1px solid #eee;
}

body h2 {
  padding-bottom: 0.3em;
  font-size: 1.5em;
  border-bottom: 1px solid #eee;
}

body h3 {
  font-size: 1.25em;
}

body h4 {
  font-size: 1em;
}

body h5 {
  font-size: 0.875em;
}

body h6 {
  font-size: 0.85em;
  color: #777;
}

body ul,
body ol {
  padding-left: 2em;
}

body ul ul,
body ul ol,
body ol ol,
body ol ul {
  margin-top: 0;
  margin-bottom: 0;
}

body li>p {
  margin-top: 16px;
}

body li+li {
  margin-top: 0.25em;
}

body dl {
  padding: 0;
}

body dl dt {
  padding: 0;
  margin-top: 16px;
  font-size: 1em;
  font-style: italic;
  font-weight: bold;
}

body dl dd {
  padding: 0 16px;
  margin-bottom: 16px;
}

body table {
  display: block;
  width: 100%;
  overflow: auto;
  border-collapse: collapse;
  border-spacing: 0;
}

body table th {
  font-weight: bold;
}

body table th,
body table td {
  padding: 6px 13px;
  /* border: 1px solid #ddd; */
  border: solid 1px #474d54;
}

/* body table tr {
  background-color: #fff;
  border-top: 1px solid #ccc;
}

body table tr:nth-child(2n) {
  background-color: #f8f8f8;
} */

body img {
  max-width: 100%;
  box-sizing: content-box;
  /* background-color: #fff; */
}

body code {
  padding: 0;
  padding-top: 0.2em;
  padding-bottom: 0.2em;
  margin: 0;
  font-size: 85%;
  background-color: rgba(0, 0, 0, 0.05);
  color: #DA924A;
  border-radius: 3px;
}

body code::before,
body code::after {
  letter-spacing: -0.2em;
  content: "\00a0";
}

body pre {
  word-wrap: normal;
}

body pre>code {
  padding: 0;
  margin: 0;
  font-size: 100%;
  word-break: normal;
  white-space: pre;
  background: transparent;
  border: 0;
}

body .highlight {
  margin-bottom: 16px;
}

body .highlight pre {
  margin-bottom: 0;
  word-break: normal;
}

body .highlight pre,
body pre {
  padding: 16px;
  overflow: auto;
  font-size: 85%;
  line-height: 1.45;
  /* background-color: #f7f7f7; */
  border-radius: 3px;
}

body pre code {
  display: inline;
  max-width: auto;
  padding: 0;
  margin: 0;
  overflow: visible;
  line-height: inherit;
  word-wrap: normal;
  background-color: transparent;
  border: 0;
}

body pre code::before,
body pre code::after {
  content: normal;
}

/* body kbd {
  display: inline-block;
  padding: 3px 5px;
  font: 11px Consolas, "Liberation Mono", Menlo, Courier, monospace;
  line-height: 10px;
  color: #555;
  vertical-align: middle;
  background-color: #fcfcfc;
  border: solid 1px #ccc;
  border-bottom-color: #bbb;
  border-radius: 3px;
  box-shadow: inset 0 -1px 0 #bbb;
} */

body hr {
  border-bottom-color: #eee;
}