BUILD A PHP CALCULATOR
<!DOCTYPE html> <html lang="en"> <head> <meta charset="UTF-8"> <meta name="viewport" content="width=device-width, initial-scale=1.0"> <meta http-equiv="X-UA-Compatible" content="ie=edge"> <title>PHP Course</title> </head> <style> h1{ color:teal; font-weight: bold; } .container{ width:400px; background-color: aqua; padding: 10px; } .first input{ display: block; } .answer{ border: 1px solid teal; padding: 10px; font-size: 16px; width:170px; margin-top: 10px; text-align: center; background: #f0f0f0; } .number{ padding:10px; font-size: 15px; } .btn{