要将元素的宽度设置为75％，请在Bootstrap中使用.w-75类。
您可以尝试运行以下代码来设置元素的宽度-
<!DOCTYPE html> <html> <head> <title>Bootstrap Example</title> <link rel = "stylesheet" href = "https://maxcdn.bootstrapcdn.com/bootstrap/4.1.1/css/bootstrap.min.css"> <script src = "https://cdn.staticfile.org/jquery/3.3.1/jquery.min.js"></script> <script src = "https://maxcdn.bootstrapcdn.com/bootstrap/4.1.1/js/bootstrap.min.js"></script> </head> <body> <div class = "container"> <h3>Set element width</h3> <div class = "w-100 bg-danger">Normal width</div> <div class = "w-75 bg-warning">Width is 75%</div> </body> </html>