content,devtools: update readme.css for goldmark styles

Updates css generator and creates new readme.css file that
preserves github heading styles when using the goldmark
parser.

Change-Id: Iddd2ea99711ffe11c14f6e9e2087b023b7d73325
Reviewed-on: https://go-review.googlesource.com/c/pkgsite/+/266580
Trust: Jamal Carvalho <jamal@golang.org>
Reviewed-by: Julie Qiu <julie@golang.org>

1 files changed, 18 insertions, 0 deletions

diff --git a/devtools/cmd/css/main.go b/devtools/cmd/css/main.go
index 6324c15b..f2de24c9 100644
--- a/devtools/cmd/css/main.go
+++ b/devtools/cmd/css/main.go
@@ -59,6 +59,9 @@ func main() {
 	)
 	for scanner.Scan() {
 		text := scanner.Text()
+		if headerString := replaceHeaderTag(text); headerString != "" {
+			text = headerString
+		}
 		if atPropertyStart && shouldIncludeProperty(text) {
 			includeProperty = true
 		}
@@ -131,6 +134,21 @@ func main() {
 	}
 }
 
+// replaceHeaderTag finds any header tags in a line of text and increases
+// the header level by 2. replaceHeader tag returns the replaced string if a
+// header tag is found and returns an empty string if not
+func replaceHeaderTag(property string) string {
+	headerMap := map[string]string{
+		"h1": "h3", "h2": "h4", "h3": "h5", "h4": "h6", "h5": "div[aria-level=7]", "h6": "div[aria-level=8]",
+	}
+	for k, v := range headerMap {
+		if strings.Contains(property, k) {
+			return strings.ReplaceAll(property, k, v)
+		}
+	}
+	return ""
+}
+
 // shouldIncludeProperty reports whether this property should be included in
 // the CSS file.
 func shouldIncludeProperty(property string) bool {