Revert "ts: Convert css_variables.js to TypeScript."

This reverts commit 5f4bdfe6bc (#24630).

This was causing Webpack to trigger type checking with the TypeScript
compiler, which is very expensive.

Signed-off-by: Anders Kaseorg <anders@zulip.com>

tools/test-js-with-node

@@ -73,7 +73,7 @@ EXEMPT_FILES = make_set(
         "web/src/confirm_dialog.js",
         "web/src/copy_and_paste.js",
         "web/src/csrf.ts",
-        "web/src/css_variables.ts",
+        "web/src/css_variables.js",
         "web/src/dark_theme.js",
         "web/src/debug.ts",
         "web/src/deprecated_feature_notice.js",

web/src/css_variables.js

@@ -0,0 +1,39 @@
+/* eslint-env commonjs */
+
+"use strict";
+
+// Media query breakpoints according to Bootstrap 4.5
+const xs = 0;
+const sm = 576;
+const md = 768;
+const lg = 992;
+const xl = 1200;
+
+// Breakpoints for mobile devices used by Google Chrome as of Version 86
+const ml = 425; // Mobile large
+const mm = 375; // Mobile medium
+const ms = 320; // Mobile small
+
+module.exports = {
+    media_breakpoints: {
+        xs_min: xs + "px",
+        sm_min: sm + "px",
+        md_min: md + "px",
+        lg_min: lg + "px",
+        xl_min: xl + "px",
+        ml_min: ml + "px",
+        mm_min: mm + "px",
+        ms_min: ms + "px",
+    },
+
+    media_breakpoints_num: {
+        xs,
+        sm,
+        md,
+        lg,
+        xl,
+        ml,
+        mm,
+        ms,
+    },
+};

web/src/css_variables.ts

@@ -1,33 +0,0 @@
-// Media query breakpoints according to Bootstrap 4.5
-const xs = 0;
-const sm = 576;
-const md = 768;
-const lg = 992;
-const xl = 1200;
-
-// Breakpoints for mobile devices used by Google Chrome as of Version 86
-const ml = 425; // Mobile large
-const mm = 375; // Mobile medium
-const ms = 320; // Mobile small
-
-export const media_breakpoints = {
-    xs_min: `${xs}px`,
-    sm_min: `${sm}px`,
-    md_min: `${md}px`,
-    lg_min: `${lg}px`,
-    xl_min: `${xl}px`,
-    ml_min: `${ml}px`,
-    mm_min: `${mm}px`,
-    ms_min: `${ms}px`,
-};
-
-export const media_breakpoints_num = {
-    xs,
-    sm,
-    md,
-    lg,
-    xl,
-    ml,
-    mm,
-    ms,
-};