* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
}
main {
    max-width: 640px;
    margin: 50px auto;
}
 h1, p {
     text-align: center;
     margin-bottom: 20px;
 }

 fieldset {
     padding: 10px;
     margin-bottom: 10px;
 }

 input {
     display: block;
     width: 100%;
     height: 30px;
 }
 button {
     display: inline-block;
     height: 30px;
     min-width: 100px;
 }
 p#hint {
     color: red;
 }