So i wrote this code with border-spacing: border-box (which some said was the solution) but still the boxes are exceeding from the right side of the padding.
html:
<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Contact Form</title>
    <link rel="stylesheet" href="stylesheet.css">
</head>
<body>
    <div class="main">
        <form action="">
            <header>
                <h1 class="up">Contact Form</h1>
                <h4 class="up">Please fill all the texts in the fields.</h4>
            </header>
            <section>
                <p class="name">Your name: <input type="text" name="name" placeholder="Your Full Name"></p>
                <p class="email">Your Email: <input type="email" name="email" id="email"
                        placeholder="Valid Email Address">
                </p>
                <p class="message">Message: <textarea name="message" id="message" cols="30" rows="10"
                        placeholder="Your message to us"></textarea></p>
                <p class="subject">Subject: <input type="text" name="subject" id="subject" placeholder="Job Inquiry">
                </p>
                <input type="submit" value="Send">
            </section>
        </form>
    </div>
</body>
</html>
css:
*{
    border-spacing: border-box;
    
}
body {
    font-family: Verdana, Geneva, Tahoma, sans-serif;
    padding: 12px;
    margin: 15px 30px;
    font-size: 17px;
}
.main {
    background-color: #f2f2f2;
    
}
header{
    background-color: #008325;
    border-radius: 5px;
    margin: none;
    padding: 30px;
    color: #f2f2f2;
}
section {
    padding: 15px;
}
input[type="text"], textarea, input[type="email"] {
    width: 100%;
    padding: 12px;
    border-radius: 5px;
    margin: 2px;
    text-overflow: auto;
}
input[type="submit"] {
    padding: 12px;
    border-radius: 5px;
    border: none;
    background-color: #005e1b;
    color: #f2f2f2;
    cursor: pointer;
}
input[type="submit"]:hover {
    background-color: #008325;
}
The input texts just don't come inside the padding
 
    