WordPress comes with some built in widgets such as recent comments, calendar, tags, categories etc. While developing a WordPress theme you need to style the default widgets too.
Here is the list of CSS classes to style the built in widgets
.widget {}
#searchform {}
.widget_search {}
.screen-reader-text {}
.widget_meta {}
.widget_meta ul {}
.widget_meta ul li {}
.widget_meta ul li a {}
.widget_links {}
.widget_links ul {}
.widget_links ul li {}
.widget_links ul li a {}
.widget_archive {}
.widget_archive ul {}
.widget_archive ul li {}
.widget_archive ul li a {}
.widget_archive select {}
.widget_archive option {}
.widget_pages {}
.widget_pages ul {}
.widget_pages ul li {}
.widget_pages ul li a {}
.widget_links {}
.widget_links li:after {}
.widget_links li:before {}
.widget_tag_cloud {}
.widget_tag_cloud a {}
.widget_tag_cloud a:after {}
.widget_tag_cloud a:before {}
.widget_calendar {}
#calendar_wrap {}
#calendar_wrap th {}
#calendar_wrap td {}
#wp-calendar tr td {}
#wp-calendar caption {}
#wp-calendar a {}
#wp-calendar #today {}
#wp-calendar #prev {}
#wp-calendar #next {}
#wp-calendar #next a {}
#wp-calendar #prev a {}
.widget_categories {}
.widget_categories ul {}
.widget_categories ul li {}
.widget_categories ul ul.children {}
.widget_categories a {}
.widget_categories select{}
.widget_categories select#cat {}
.widget_categories select.postform {}
.widget_categories option {}
.widget_categories .level-0 {}
.widget_categories .level-1 {}
.widget_categories .level-2 {}
.widget_categories .level-3 {}
.recentcomments {}
#recentcomments {}
#recentcomments li {}
#recentcomments li a {}
.widget_recent_comments {}
.widget_recent_entries {}
.widget_recent_entries ul {}
.widget_recent_entries ul li {}
.widget_recent_entries ul li a {}
.textwidget {}
.widget_text {}
.textwidget p {}
#searchform {}
.widget_search {}
.screen-reader-text {}
.widget_meta {}
.widget_meta ul {}
.widget_meta ul li {}
.widget_meta ul li a {}
.widget_links {}
.widget_links ul {}
.widget_links ul li {}
.widget_links ul li a {}
.widget_archive {}
.widget_archive ul {}
.widget_archive ul li {}
.widget_archive ul li a {}
.widget_archive select {}
.widget_archive option {}
.widget_pages {}
.widget_pages ul {}
.widget_pages ul li {}
.widget_pages ul li a {}
.widget_links {}
.widget_links li:after {}
.widget_links li:before {}
.widget_tag_cloud {}
.widget_tag_cloud a {}
.widget_tag_cloud a:after {}
.widget_tag_cloud a:before {}
.widget_calendar {}
#calendar_wrap {}
#calendar_wrap th {}
#calendar_wrap td {}
#wp-calendar tr td {}
#wp-calendar caption {}
#wp-calendar a {}
#wp-calendar #today {}
#wp-calendar #prev {}
#wp-calendar #next {}
#wp-calendar #next a {}
#wp-calendar #prev a {}
.widget_categories {}
.widget_categories ul {}
.widget_categories ul li {}
.widget_categories ul ul.children {}
.widget_categories a {}
.widget_categories select{}
.widget_categories select#cat {}
.widget_categories select.postform {}
.widget_categories option {}
.widget_categories .level-0 {}
.widget_categories .level-1 {}
.widget_categories .level-2 {}
.widget_categories .level-3 {}
.recentcomments {}
#recentcomments {}
#recentcomments li {}
#recentcomments li a {}
.widget_recent_comments {}
.widget_recent_entries {}
.widget_recent_entries ul {}
.widget_recent_entries ul li {}
.widget_recent_entries ul li a {}
.textwidget {}
.widget_text {}
.textwidget p {}
