Update

after/syntax/html.vim

@@ -9,6 +9,28 @@ syn region coffeeScript start=#<script [^>]*type="text/coffeescript"[^>]*>#
 \                       end=#</script>#me=s-1 keepend
 \                       contains=@htmlCoffeeScript,htmlScriptTag,@htmlPreproc
 \                       containedin=htmlHead
+if !exists("g:less_html_style_tags")
+  let g:less_html_style_tags = 1
+endif
+
+if !g:less_html_style_tags
+  finish
+endif
+
+" Unset (but preserve) so that less will run.
+let s:pre_less_cur_syn = b:current_syntax
+unlet b:current_syntax
+
+" Inspired by code from github.com/kchmck/vim-coffee-script
+" and the html syntax file included with vim 7.4.
+
+syn include @htmlLess syntax/less.vim
+
+" We have to explicitly add to htmlHead (containedin) as that region specifies 'contains'.
+syn region lessStyle start=+<style [^>]*type *=[^>]*text/less[^>]*>+ keepend end=+</style>+ contains=@htmlLess,htmlTag,htmlEndTag,htmlCssStyleComment,@htmlPreproc containedin=htmlHead
+
+" Reset since 'less' isn't really the current_syntax.
+let b:current_syntax = s:pre_less_cur_syn
 " Language:     Colorful CSS Color Preview
 " Author:       Aristotle Pagaltzis <pagaltzis@gmx.de>
 

after/syntax/rust.vim

@@ -29,5 +29,3 @@ hi link rustNiceOperator Operator
 if !exists('g:rust_conceal_mod_path')
     hi! link Conceal Operator
 endif
-
-setlocal conceallevel=2