.sanJiao-top {
width: 0;
height: 0;
border-bottom: 50px solid red;
border-left: 50px solid transparent;
border-right: 50px solid transparent;
}
原理参考：https://blog.csdn.net/pengjunlee/article/details/53002553?ops_request_misc=%257B%2522request%255Fid%2522%253A%2522168376741016782425177038%2522%252C%2522scm%2522%253A%252220140713.130102334..%2522%257D&request_id=168376741016782425177038&biz_id=0&utm_medium=distribute.pc_search_result.none-task-blog-2~all~sobaiduend~default-1-53002553-null-null.142^v86^insert_down1,239^v2^insert_chatgpt&utm_term=html%E4%B8%89%E8%A7%92%E5%BD%A2%E5%8E%9F%E7%90%86&spm=1018.2226.3001.4187
标签：实现,2522%,50px,utm,solid,html,三角形,border,id From： https://www.cnblogs.com/xiaoming626/p/17390008.html