css: Add new css for rendered markdown table in dark mode.

Add a new dark mode css in app_variable.css for rendered
markdown tables. This rule sets a brighter color for tables
in messages / chat to make it more visible when the user is
using dark theme.

Fixes #29856.

web/styles/app_variables.css

@@ -785,6 +785,9 @@
     --color-border-emoji-picker-emoji-reacted: hsl(0deg 0% 0% / 90%);
     --color-background-emoji-picker-emoji-reacted-focus: hsl(0deg 0% 20% / 70%);
     --color-border-add-subscription-button-focus: hsl(0deg 0% 67%);
+
+    /* Rendered markdown table color (dark) */
+    --border-rendered-markdown-tr-th-td: 1px solid hsl(0deg 0% 100% / 20%);
 }
 
 @media screen {

web/styles/dark_theme.css

@@ -786,9 +786,6 @@
     #subscription_overlay .settings-radio-input-parent,
     #settings_page .sidebar-wrapper,
     #settings_page .sidebar-wrapper *,
-    table,
-    table th,
-    table td,
     #recent_view_table table td {
         border-color: hsl(0deg 0% 0% / 20%);
     }