<!DOCTYPE html><html lang="en"><head> ???<meta charset="UTF-8"> ???<style> ???????input:focus{ ???????????outline: red 1px solid; ???????} ???</style> ???<title>outline</title></head><body><input type="text"></body></html>当input框获取焦点时，边框变红
02.CSS选择器-->:focus
原文地址：http://www.cnblogs.com/ronghtp/p/7647329.html