Improve HTML highlighting (#10503)

runtime/themes/horizon-dark.toml

@@ -4,15 +4,19 @@ constant = "purple"
 "constant.numeric" = "orange"
 "constant.builtin" = "orange"
 variable = "red"
+attribute = "brown"
 comment = "light-gray"
 special = "purple"
+"punctuation" = "red"
 "punctuation.bracket" = "purple"
+"punctuation.delimiter" = "white"
 keyword = "purple"
 function = "blue"
 label = "orange"
 type = "orange"
 constructor = "orange"
 namespace = "orange"
+tag = "red"
 
 # User Interface
 "ui.background" = { bg = "bg", fg = "gray" }
@@ -79,6 +83,7 @@ pink = "#EE64AE"
 selection = "#353747"
 green = "#27D796"
 orange = "#FAB795"
+brown = "#F09383"
 purple = "#B877DB"
 red = "#E95678"
 blue = "#25B2BC"