Remove :not pseudo-class from md-table styles

Rollback change that adds :not(js-syntax-highlight) pseudo-class
to markdown selectors to fix syntax highlight tables in
MR code suggestions. Removes redundant inclusion of
md-typography mixin as an alternative fix.

app/assets/stylesheets/framework/markdown_area.scss

@@ -150,7 +150,7 @@
   }
-  table:not(.js-syntax-highlight) {
+  table {
     @include markdown-table;
   }
 }

app/assets/stylesheets/framework/mixins.scss

@@ -29,15 +29,14 @@
   display: block;
   overflow-x: auto;
   border: 0;
-  border-color: $gl-gray-100;
   tr {
     th {
-      border-bottom: solid 2px $gl-gray-100;
+      border-bottom: solid 2px $gl-gray-200;
     }
     td {
-      border-color: $gl-gray-100;
+      border-color: $gl-gray-200;
     }
   }
 }

app/assets/stylesheets/framework/typography.scss

@@ -136,15 +136,21 @@
     margin: 0 0 16px;
   }
-  table:not(.js-syntax-highlight) {
+  table {
     @extend .table;
     @extend .table-bordered;
     margin: 16px 0;
     color: $gl-text-color;
     border: 0;
-    th {
-      background: $label-gray-bg;
+    tr {
+      th {
+        border-bottom: solid 2px $gl-gray-200;
+      }
+
+      td {
+        border-color: $gl-gray-200;
+      }
     }
   }

app/assets/stylesheets/pages/notes.scss

@@ -224,14 +224,9 @@ $note-form-margin-left: 72px;
       overflow-y: hidden;
       .note-text {
-        @include md-typography;
         // Reset ul style types since we're nested inside a ul already
         @include bulleted-list;
         word-wrap: break-word;
-
-        table {
-          @include markdown-table;
-        }
       }
     }

changelogs/unreleased/57655-fix-markdown-tables-border.yml

+---
+title: Fix markdown table header and table content borders
+merge_request: 25666
+author:
+type: fixed