Plugin: How i can make a button to download a backup of option database?

Hi! How i can make a function in my plugin to permit a download of sql backup from css table (my plugin permit to insert custom css – in database is “wp_options`; my_custom_css”). I’m glad, if is possible, to make simply a button (a little form) and a query/function to save/download simply with my_custom_css_bkk.css 🙂