apply theme color to slider in MarkdownSplitEditor

Author: amedora

browser/components/MarkdownSplitEditor.styl

@@ -8,9 +8,30 @@
     top -2px
     width 0
     z-index 0
+    border-left 1px solid $ui-borderColor
   .slider-hitbox
     absolute top bottom left right
     width 7px
     left -3px
     z-index 10
     cursor col-resize
+
+body[data-theme="dark"]
+  .root
+    .slider
+      border-left 1px solid $ui-dark-borderColor
+
+body[data-theme="solarized-dark"]
+  .root
+    .slider
+      border-left 1px solid $ui-solarized-dark-borderColor
+
+body[data-theme="monokai"]
+  .root
+    .slider
+      border-left 1px solid $ui-monokai-borderColor
+
+body[data-theme="dracula"]
+  .root
+    .slider
+      border-left 1px solid $ui-dracula-borderColor