修改文本框和文本域placeholder样式

 input::-webkit-input-placeholder, textarea::-webkit-input-placeholder {
            font-size:20px;
            padding:20px;
            font-family:PingFang SC;
            font-weight:300;
            color:rgba(255,255,255,0.4);
        }
        input:-moz-placeholder, textarea:-moz-placeholder {
            font-size:20px;
            font-family:PingFang SC;
            padding:20px;
            font-weight:300;
            color:rgba(255,255,255,0.4);
        }
        input::-moz-placeholder, textarea::-moz-placeholder {
            font-size:20px;
            padding:20px;
            font-family:PingFang SC;
            font-weight:300;
            color:rgba(255,255,255,0.4);
        }
        input:-ms-input-placeholder, textarea:-ms-input-placeholder {
            font-size:20px;
            padding:20px;
            font-family:PingFang SC;
            font-weight:300;
            color:rgba(255,255,255,0.4);
        }
        ```