Force normal font weight in <th> elements

The <th> are produced by LaTeXML in somewhat mysterious ways, and this really messes up the look of tables due to the default browser behavior of using bold font weight for these elements.  This commit is a workaround for this styling problem.

Makefile

@@ -24,4 +24,4 @@ MLS.pdf: *.tex chapters/*.tex
 # Not using %.html since nmake does not support it (instead using old-style suffix rules)
 MLS.html: MLS.tex chapters/*.tex
 	$(LATEXMLPREFIX)latexml MLS.tex --path=media --dest MLS.xml
-	$(LATEXMLPREFIX)latexmlpost MLS.xml -format html -pmml --splitat=chapter --splitnaming=labelrelative --javascript=css/LaTeXML-maybeMathJax.js --navigationtoc=context --css=css/LaTeXML-navbar-left.css --dest $@
+	$(LATEXMLPREFIX)latexmlpost MLS.xml -format html -pmml --splitat=chapter --splitnaming=labelrelative --javascript=css/LaTeXML-maybeMathJax.js --navigationtoc=context --css=css/MLS.css --css=css/LaTeXML-navbar-left.css --dest $@

css/MLS.css

@@ -0,0 +1,7 @@
+/* This CSS makes adjustments for the MLS on top of the style sheets that come with LaTeXML.
+ * By not editing copies of the ones from LaTeXML, we can take advantage of upstream improvements to the LaTeXML files.
+ */
+
+/* Undo bold here to remove the browser's native th styling,
+ */
+.ltx_th { font-weight:normal; }