Improve arc-green code colors (#12111)

* Improve arc-green code colors

This should fix all previous colors that had too few contrast on the
background. I took solarized-dark as a baseline and did various
improvments. I removed bold/italic flags because I don't think they
fit and generally other tools also don't use those font flags.

* diff tweak

Author: silverwind

web_src/less/_chroma.less

@@ -221,7 +221,6 @@
 /* LiteralStringRegex */
 
 .chroma .sr {
-    font-weight: bold;
     color: #22863a;
 }
 /* LiteralStringSingle */
@@ -303,7 +302,6 @@
 
 .chroma .cs {
     color: #999999;
-    font-style: italic;
 }
 /* CommentPreproc */
 
@@ -325,7 +323,6 @@
 
 .chroma .ge {
     color: #000000;
-    font-style: italic;
 }
 /* GenericError */