Ключевые слова: 3d, app, background, book, bookstore, button, color, cover, design, digital, document, education, element, encyclopedia, flat, graphic, icon, illustration, infographic, internet, isolated, isometric, knowledge, learning, library, line, literature, next, object, open, open book, outline, paper, perspective, pictogram, reading, school, science, set, sign, stack, stroke, study, symbol, textbook, thin, university, web,