body {
    margin: 0;
    padding: 0;
    font-family: sans-serif;
    background: url('../img/bg.jpg') !important;
    background-size: cover;
}

.box {
    position: absolute;
    top: 50%;
    left: 50%;
    transform: translate(-50%, -50%);
    min-width: 325px;
    width: 60%;
    padding: 4%;
    background: rgba(0, 0, 0, 0.5);
    box-sizing: border-box;
    box-shadow: 0 15px 20px rgba(0, 0, 0, 0.5);
    border-radius: 10px;
}

.box h2 {
    margin: 0 0 30px;
    padding: 0px;
    color: #fff;
    text-align: center;
    letter-spacing: 3px;
}

.box .input-box {
    position: relative;
}

.box .input-box input {
    width: 100%;
    padding: 10px 0;
    font-size: 16px;
    color: #fff;
    letter-spacing: 1px;
    margin-bottom: 30px;
    border: none;
    outline: none;
    background: transparent;
    border-bottom: 1px solid #fff;
}

.box .input-box label {
    position: absolute;
    top: 0;
    left: 0;
    letter-spacing: 1px;
    padding: 10px 0px;
    font-size: 16px;
    font-weight: bold;
    color: #fff;
    transition: .5s;
}

.box .input-box input:focus~label,
.box .input-box input:valid~label {
    top: -25px;
    left: 0;
    color: #fff;
    font-size: 12px;
}

.box input[type="submit"] {
    background: transparent;
    border: none;
    outline: none;
    color: #fff;
    background: #227be3;
    padding: 10px 20px;
    border-radius: 5px;
    cursor: pointer;
}
@media (max-width: 500px) {
    .top h2 {
        font-size: 1rem;
    }
    .nb {
        font-size: 1.2rem;
    }
}