transparent为透明
<!DOCTYPE html> <html lang="en"> <head> <meta charset="UTF-8"> <title>important属性介绍</title> <style type="text/css"> div{ width:0; height: 0; border-top: 20px solid red; border-left: 20px solid transparent; border-right: 20px solid transparent; } </style> </head> <body> <div> </div> </body> </html>