前端部分：first:<input type="text" id="first">first3:<input type="text" id="first3"><button onclick="btn()">提交</button>first1:<input type="text" name="first1" id="result">...

献上效果图：代码<div class="box"></div>CSS：.box {width: 300px;height: 0;border-width: 0px 150px 150px 0px;border-style: none solid solid;border-color: transparent transparent rgba(255, 0, 0, 1);}解