@rootNov 09.2016 — #for example, in the head of your HTML [code=html]<link type="text/css" rel="stylesheet" href="../base.css" id="the_theme" />[/code] then with your button, add an onclick event handler to call a function function changit(){ document.getElementById('the_theme').href = '../alternative.css'; }
That should allow you to change the theme, to give multiple choices, your options are to use a drop down menu that calls and changes when selected.
Why answer with the same answer as mine unless you are trying to bump your post count...
You should also read the webdeveloper site AUP about posting links in signatures advertising stuff... unless you have permission to post them, you should refrain from doing so.