dark_plus: Add the borders color from the original theme (#2186)

runtime/themes/dark_plus.toml

@@ -78,7 +78,8 @@
 "ui.text" = { fg = "text" }
 "ui.text.focus" = { fg = "white" }
 
-"ui.virtual" = { fg = "dark_green" }
+"ui.virtual" = { fg = "dark_gray" }
+"ui.virtual.ruler" = { bg = "borders" }
 
 "warning" = { fg = "gold2" }
 "error" = { fg = "red" }
@@ -117,3 +118,4 @@ background = "#1e1e1e"
 text = "#d4d4d4"
 cursor = "#a6a6a6"
 widget = "#252526"
+borders = "#323232"