@page and @left-middle crashes the parser

[edi9999]

Expected Behaviour

@page {
    @left-middle {
        margin: 0;
    }
}

should parse without an error

Actual Behaviour

It throws the following :

input.css:29:5: @page missing '}'

  77 |
  78 |   function error(msg: string) {
> 79 |     const err = new CssParseError(
     |                 ^
  80 |       options?.source || '',
  81 |       msg,
  82 |       lineno,

  at error (src/parse/index.ts:79:17)
  at atpage (src/parse/index.ts:562:14)
  at atrule (src/parse/index.ts:693:7)
  at rules (src/parse/index.ts:134:59)
  at stylesheet (src/parse/index.ts:98:23)
  at parse (src/parse/index.ts:720:20)
  at parseInput (test/cases.test.ts:39:19)
  at Object.<anonymous> (test/cases.test.ts:31:36)

Reproduce Scenario (including but not limited to)

Apply following git patch :

diff --git a/test/cases/media/input.css b/test/cases/media/input.css
index 8ab3a73..fa567e0 100644
--- a/test/cases/media/input.css
+++ b/test/cases/media/input.css
@@ -24,3 +24,9 @@
     border: 0.5pt solid #666;
   }
 }
+
+@page {
+    @left-middle {
+        margin: 0;
+    }
+}

Steps to Reproduce

Run npm test in the css-tools repository

Platform and Version

Sample Code that illustrates the problem

Logs taken while reproducing problem

[jogibear9988]

they are not yet supported in any browser.
For me it's also not clear how they will be represented in the CSS Object Model.
Is the order of them relevant? can they appeaer everywhere inside of @page or only at the start or the end? (If they could anywhere we need to store the order)