1.Universal selectors
eg:#target*{ }
2.Child selectors <
something immediately nested within something直接子女，不包括子孙
3.Adjacent Selector +
something immediately following something 直接跟在后面的第一个跟屁虫
CSS3：h1 ~ p { font-weight: bold } will style all paragraphs after the top-level heading but if there were any ps preceding the h1, these would not be affected.