body {
    /* uigradients.com */
    background: #bdc3c7;  /* fallback for old browsers */
    background: -webkit-linear-gradient(to top, #2c3e50, #bdc3c7);  /* Chrome 10-25, Safari 5.1-6 */
    background: linear-gradient(to top, #2c3e50, #bdc3c7); /* W3C, IE 10+/ Edge, Firefox 16+, Chrome 26+, Opera 12+, Safari 7+ */
    background-repeat: no-repeat;
    height: 100vh;
    display: flex;
    flex-direction: column;
    align-items: center;
    font-family: Oxygen, sans-serif;
}

button {
    height: 100px;
    width: 100px;
    border-radius: 50%;
    background-color: red;
    border: 1px solid darkred;
    cursor: pointer;
}

.fun {
    /* CSS generated from https://uigradients.com */
    background: #fc4a1a;  /* fallback for old browsers */
    background: -webkit-linear-gradient(to left, #f7b733, #fc4a1a);  /* Chrome 10-25, Safari 5.1-6 */
    background: linear-gradient(to left, #f7b733, #fc4a1a); /* W3C, IE 10+/ Edge, Firefox 16+, Chrome 26+, Opera 12+, Safari 7+ */
}