style.css

body {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
}

button:focus {outline:0;}
.container {
    margin: 30px 20vh;
    text-align: center;
}

main {
    text-align: center;
}
.box-choice-numbers {
    display: flex;
    max-width: 350px;
    flex-wrap: wrap;
}
.box-choice-numbers > span {
    padding: 10px;
    border-radius: 40px;
    background-color: #307b07;
    width: 40px;
    height: 40px;
    color: white;
    display: flex;
    align-items: center;
    justify-content: center;
    margin: 5px;
}

.selected {
    color: white;
    background-color: black;
    border-radius: 40px;
    padding: 10px;
}
.btn-generate {
    background-color: #307b07;
    padding: 10px;
    border-radius: 10px;
    border: 0;
    color: white;
    font-weight: 400;
    width: 100px;
    font-size: 18px;
    font-family: 'Roboto', sans-serif;
    display:inline-block;
    text-decoration:none;
    cursor: pointer;
}

.btn-generate:active {
    position:relative;
	top:1px;
}
.btn-generate:hover {
    background-color: #205706;
    transition: 1.5ms;
}