fix: use CSS Custom Highlight API to avoid dom modifications (fixes #1)

src/types/css-highlights.d.ts

@@ -0,0 +1,27 @@
+// CSS Highlights API type declarations
+interface Highlight {
+  new(...ranges: Range[]): Highlight;
+  add(range: Range): void;
+  clear(): void;
+  delete(range: Range): boolean;
+  has(range: Range): boolean;
+  readonly size: number;
+}
+
+interface HighlightRegistry {
+  set(name: string, highlight: Highlight): void;
+  get(name: string): Highlight | undefined;
+  delete(name: string): boolean;
+  clear(): void;
+  has(name: string): boolean;
+  readonly size: number;
+}
+
+interface CSS {
+  highlights: HighlightRegistry;
+}
+
+declare var Highlight: {
+  prototype: Highlight;
+  new(...ranges: Range[]): Highlight;
+};