register_sidebar(array(
        'name' => 'Sidebar',
        'before_widget' => '<li id="%1$s" class="widget %2$s">',
        'after_widget' => '</li>',
        'before_title' => '<h2 class="widgettitle">',
        'after_title' => '</h2>'
    ));

You can change the values to your need.

Encouragements,

this page uses some widget to show the previous post name and the next post name, how do you do it? using this widget?

thanks,