Automatically apply custom chroma theme when set in style

ansi/codeblock.go

@@ -63,6 +63,8 @@ func (e *CodeBlockElement) Render(w io.Writer, ctx RenderContext) error {
 	}
 	theme := rules.Theme
 
+	if rules.Chroma != nil {
+		theme = "charm"
 		styles.Register(chroma.MustNewStyle("charm",
 			chroma.StyleEntries{
 				chroma.Text:                chromaStyle(rules.Chroma.Text),
@@ -97,6 +99,7 @@ func (e *CodeBlockElement) Render(w io.Writer, ctx RenderContext) error {
 				chroma.GenericSubheading:   chromaStyle(rules.Chroma.GenericSubheading),
 				chroma.Background:          chromaStyle(rules.Chroma.Background),
 			}))
+	}
 
 	iw := &indent.Writer{
 		Indent: indentation + margin,

ansi/style.go

@@ -38,7 +38,7 @@ type StyleBlock struct {
 type StyleCodeBlock struct {
 	StyleBlock
 	Theme  string `json:"theme"`
-	Chroma struct {
+	Chroma *struct {
 		Text                StylePrimitive `json:"text"`
 		Error               StylePrimitive `json:"error"`
 		Comment             StylePrimitive `json:"comment"`