Stylize horizon-dark picker v2 columns (#11649)

runtime/themes/horizon-dark.toml

@@ -43,6 +43,8 @@ tag = "red"
 "ui.bufferline" = { bg = "dark-bg", fg = "light-gray" }
 "ui.bufferline.active" = { bg = "dark-bg", fg = "orange" }
 "ui.virtual.jump-label" = { fg = "pink", modifiers = ["bold"] }
+"ui.picker.header.column" = { fg = "orange", underline.style = "line" }
+"ui.picker.header.column.active" = { fg = "purple", modifiers = ["bold"], underline.style = "line" }
 
 # Diagnostics
 "diagnostic" = { underline = { style = "curl" } }