使用css把placeholder值渐渐消失

复制过去就行了，不要问我为什么，就两个字爽快
input:focus {outline: none; }
input:focus::-webkit-input-placeholder {text-indent: 100%; opacity: 0; -webkit-transition: .4s; transition: .4s; }
input:focus::-moz-placeholder {text-indent: 100%; opacity: 0; -moz-transition: .4s; }
input:focus:-ms-input-placeholder {text-indent: 100%; opacity: 0; -webkit-transition: .4s; transition: .4s; }
textarea:focus {outline: none; }
textarea:focus::-webkit-input-placeholder {text-indent: 100%; opacity: 0; -webkit-transition: .4s; transition: .4s; }
textarea:focus::-moz-placeholder {text-indent: 100%; opacity: 0; -moz-transition: .4s; }
textarea:focus:-ms-input-placeholder {text-indent: 100%; opacity: 0; -webkit-transition: .4s; transition: .4s; }