Add configuration

highlight.go

@@ -13,6 +13,8 @@ import (
 
 const reviewContextLines = 3
 
+var codeHighlightTheme = "github-dark"
+
 var hunkHeaderPattern = regexp.MustCompile(`^@@ -(\d+)(?:,\d+)? \+(\d+)(?:,\d+)? @@`)
 
 type highlightedDiffLine struct {
@@ -223,7 +225,7 @@ func coordinateText(line int) string {
 
 func highlightedSource(lexer, source string) string {
 	var highlighted bytes.Buffer
-	if err := quick.Highlight(&highlighted, source, lexer, "terminal16m", "github-dark"); err != nil {
+	if err := quick.Highlight(&highlighted, source, lexer, "terminal16m", codeHighlightTheme); err != nil {
 		return source
 	}
 	return strings.TrimSuffix(highlighted.String(), "\n")