estilo.css

body {
    background-image: url(fondo.jpg);
    background-size: 1990px;
}

button {
    font-size: 20px;
    background-color: #5F5654;
    box-shadow: 50px 13px 37px #000;
    color: #fff;
    width: 100px;
    margin: 46px;
    margin-top: 40px;
    border: color white 3px;
}

form {
    box-shadow: 10px 13px 37px #000;
    padding: 50px 20px;
    margin: calc(25% + 90px);
    margin-top: 0px;
    padding-top: 28px;
    margin-bottom: 30px
}

input {
    background-color: transparent;
    width: calc(100% - 20px);
    padding: 9px;
    margin: auto;
    margin-top: 12px;
    font-size: 16px;
}

input[type='submit'] {
    background-color: #3B3737;
    box-shadow: 10px 13px 37px #000;
    color: #fff;
    width: calc(50% - 20px);
    margin: 0 30%;
    margin-top: 30px;
    border: color white 3px;
}

body>form {
    margin-top: 80px;
}

body>form>select {
    margin-top: 10px;
    width: 50px;
    height: 30px;
}