body {
    position: relative;
    width: 100%;
    margin: 0;
    height: 100vh;
    background-repeat: no-repeat;
    background-size: cover;
    background-position: center center;
    overflow: hidden;
}

* {
    font-family: 'Roboto', sans-serif;
    box-sizing: border-box;
}

.index {
    background-image: url(https://d1fmx1rbmqrxrr.cloudfront.net/zdnet/i/edit/ne/2016/02/Art2-flux-data-600.jpg);
}

.flask {
    background-image: url(https://images.pexels.com/photos/241544/pexels-photo-241544.jpeg?auto=compress&cs=tinysrgb&h=750&w=1260);
}

.base_donnee {
    background-image: url(https://images.unsplash.com/photo-1610648888194-e410f3d6828b?ixid=MXwxMjA3fDB8MHx0b3BpYy1mZWVkfDU3fEo5eXJQYUhYUlFZfHxlbnwwfHx8&ixlib=rb-1.2.1&auto=format&fit=crop&w=500&q=60);
}

.calculatrice {
    background-image: url(https://images.pexels.com/photos/1314543/pexels-photo-1314543.jpeg?auto=compress&cs=tinysrgb&dpr=1&w=500);
}

.page {
    position: relative;
    height: 100vh;
    width: 100%;
    display: flex;
    align-items: center;
    align-content: center;
    flex-direction: column;
    padding: 20px;
    padding-top: 70px;
    box-sizing: border-box;
    overflow-y: auto;
}

.page>* {
    margin: auto;
}

h1,
h2,
h3,
p,
a {
    color: rgba(0, 0, 0, 0.8);
}

hr {
    border: 0;
    border-top: 1px solid rgba(0, 0, 0, 0.05);
}

.button {
    display: inline-block;
    padding: 10px 20px;
    background: rgba(0, 0, 0, 0.1);
    border: 0;
    border-radius: 5px;
    font-size: 16px;
    margin: 10px;
    text-decoration: none;
}

[disabled] {
    opacity: 0.3;
}

@media screen and (max-width: 500px) {
    .button {
        margin: 5px 10px;
    }
    .or {
        display: inline-block;
        width: 100%;
    }
}