Add markdown support

app/javascript/styles/application.scss

@@ -23,3 +23,4 @@
 @import 'mastodon/dashboard';
 @import 'mastodon/rtl';
 @import 'mastodon/accessibility';
+@import 'mastodon/rich_text';

app/javascript/styles/mastodon/rich_text.scss

@@ -0,0 +1,97 @@
+.account__header__bio,
+.status__content__text,
+.e-content,
+.reply-indicator__content {
+  pre,
+  blockquote {
+    margin-bottom: 20px;
+    white-space: pre-wrap;
+    unicode-bidi: plaintext;
+
+    &:last-child {
+      margin-bottom: 0;
+    }
+  }
+
+  code, pre {
+    border: 1px solid $ui-primary-color;
+    font-family: monospace;
+  }
+
+  code {
+    margin: 0 4px;
+  }
+
+  pre {
+    padding: 4px 8px;
+
+    span.ellipsis::after {
+      content: "";
+    }
+
+    span.invisible {
+      display: inline;
+      font-size: inherit;
+      line-height: inherit;
+      width: inherit;
+      height: inherit;
+      position: static;
+    }
+  }
+
+  blockquote {
+    padding-left: 10px;
+    border-left: 3px solid $darker-text-color;
+    color: $darker-text-color;
+    white-space: normal;
+
+    p:last-child {
+      margin-bottom: 0;
+    }
+  }
+
+  & > ul,
+  & > ol {
+    margin-bottom: 20px;
+  }
+
+  b,
+  strong {
+    font-weight: 700;
+  }
+
+  em,
+  i {
+    font-style: italic;
+  }
+
+  ul,
+  ol {
+    margin-left: 2em;
+
+    p {
+      margin: 0;
+    }
+  }
+
+  ul {
+    list-style-type: disc;
+  }
+
+  ol {
+    list-style-type: decimal;
+  }
+
+  mark {
+    background-color: $ui-highlight-color;
+    color: $ui-secondary-color;
+    padding: 0 2px;
+  }
+}
+
+.reply-indicator__content {
+  blockquote {
+    border-left-color: $inverted-text-color;
+    color: $inverted-text-color;
+  }
+}