Copy Bikeshed's var-click-highlighting.css to standard.css

See whatwg/html#11392 (comment), 6th bullet.

Author: jmdyck

resources.whatwg.org/standard-service-worker.js

@@ -8,7 +8,7 @@
 
 const standardShortname = location.host.split(".")[0];
 
-const cacheKey = "v12";
+const cacheKey = "v13";
 const toCache = [
   location.origin + "/",
   "https://resources.whatwg.org/spec.css",

resources.whatwg.org/standard.css

@@ -525,3 +525,46 @@ pre > code.css, pre.highlight.lang-css {
     width: 2.3em;
   }
 }
+
+/* https://github.com/speced/bikeshed/blob/main/bikeshed/stylescript/var-click-highlighting.css: */
+/*
+Colors were chosen in Lab using https://nixsensor.com/free-color-converter/
+D50 2deg illuminant, L in [0,100], a and b in [-128, 128]
+0 = lab(85,0,85)
+1 = lab(85,80,30)
+2 = lab(85,-40,40)
+3 = lab(85,-50,0)
+4 = lab(85,5,15)
+5 = lab(85,-10,-50)
+6 = lab(85,35,-15)
+
+For darkmode:
+0 = oklab(50%   0%  108%)
+1 = oklab(50% -51%   51%)
+2 = oklab(50% -64%  -20%)
+3 = oklab(50%   6%   19%)
+4 = oklab(50% -12%  -64%)
+5 = oklab(50%  44%  -19%)  
+6 = oklab(50% 102%   38%)
+*/
+
+[data-algorithm] var { cursor: pointer; }
+var[data-var-color] { background-color: var(--var-bg); box-shadow: 0 0 0 2px var(--var-bg); }
+
+var[data-var-color] { --var-bg: #F4D200; }
+var[data-var-color="1"] { --var-bg: #FF87A2; }
+var[data-var-color="2"] { --var-bg: #96E885; }
+var[data-var-color="3"] { --var-bg: #3EEED2; }
+var[data-var-color="4"] { --var-bg: #EACFB6; }
+var[data-var-color="5"] { --var-bg: #82DDFF; }
+var[data-var-color="6"] { --var-vg: #FFBCF2; }
+
+@media (prefers-color-scheme: dark) {
+  var[data-var-color] { --var-bg: #bc1a00; }
+  var[data-var-color="1"] { --var-bg: #007f00; }
+  var[data-var-color="2"] { --var-bg: #008698; }
+  var[data-var-color="3"] { --var-bg: #7f5b2b; }
+  var[data-var-color="4"] { --var-bg: #004df3; }
+  var[data-var-color="5"] { --var-bg: #a1248a; }
+  var[data-var-color="6"] { --var-vg: #ff0000; }
+}