embed bootstrap css

internal/writing/html/writer_test.go

@@ -77,9 +77,8 @@ func TestWriter_Render(t *testing.T) {
 		`<meta charset="utf-8">`,
 		`<meta name="viewport" content="width=device-width, initial-scale=1">`,
 		`<title>Tax report</title>`,
-		`https://cdn.jsdelivr.net/npm/[email protected]/dist/css/bootstrap.min.css`,
-		`integrity="`,
-		`crossorigin="anonymous"`,
+		`<style>`,
+		`Bootstrap  v5.3.3`,
 		`<main class="container-fluid py-4">`,
 		`<h1>Tax report</h1>`,
 		`<div class="table-responsive">`,
@@ -105,6 +104,15 @@ func TestWriter_Render(t *testing.T) {
 		t.Errorf("expected raw <table> tag in output\nGot:\n%s", got)
 	}
 
+	// The document must be fully self-contained: no external stylesheet
+	// <link> and no CDN reference anywhere.
+	if strings.Contains(got, "<link") {
+		t.Errorf("expected no external stylesheet <link>; document must be self-contained\nGot:\n%s", got)
+	}
+	if strings.Contains(got, "cdn.jsdelivr.net") {
+		t.Errorf("expected no CDN references; document must be self-contained\nGot:\n%s", got)
+	}
+
 	// Generated timestamp must be valid RFC3339 UTC.
 	startIdx := strings.Index(got, "Generated at ")
 	if startIdx == -1 {