body {
    margin: 0;
    text-align: center;
}

h1 {
    margin: 0 auto 1em;
    padding: 1em;
    background: #0d47a1;
    box-shadow: 0 0 15px 2px rgba(0,0,0, .6);
    font: bold 3em sans-serif;
    color: white;
}

form {
    margin: 0 auto 4em;
    width: 50%;
    max-width: 30em;
    padding: 50px 50px 25px;
    font: 120% arial;
    text-align: center;
    background: white;
    box-shadow: 0 5px 20px 1px rgba(0, 0, 0, 0.2), 0 6px 20px 0 rgba(0, 0, 0, 0.19);
}

#response {
    margin: 1em 0;
    font-size: 90%;
    border-radius: 5px;
    padding: 1em;
}

.invalid {
    background: rgb(255, 150, 150);
    color: rgb(200, 0, 0);
}

.valid {
    color: gray;
    background: rgb(220, 220, 220);
}

.rightAnswer {
    background: lightgreen;
    color: green;
}

#input_text {
    box-sizing: border-box;
    border: 1px solid lightgray;
    width: 2.5em;
    height: 2em;
    margin: .3em 0;
    text-align: center;
    font-size: 300%;
}

#input_text:hover {
    box-shadow: 0px 0px 15px 2px rgba(0, 0, 0, 0.2);
    border: 1px solid #2196f3;
}

#input_text:focus {
    box-shadow: 0px 0px 15px 2px rgba(0, 0, 0, 0.2);
    border:  2px solid #2196f3;
}

#input_text:disabled {
    background: rgb(250,250,250);
}

button {
    background: #2196f3;
    padding: .5em 2em;
    width: 100%;
    color: white;
    font-size: 100%;
    border: 0px;
}

button:hover{
    box-shadow: 0px 0px 20px 2px rgba(0, 0, 0, 0.2);
    cursor: auto;
}