* {
    margin: 0px;
    padding: 0px;
    box-sizing: border-box;
}

body {
    display: flex;
    flex-flow: row wrap;
    background-color: skyblue;
    justify-content: center;
    font-family: Arial, Helvetica, sans-serif;
}

header {
    width: 100%;
    padding: 20px;
    margin: 20px;
    text-align: center;
    line-height: 5em;
}

h1 {
    font-size: 80px;
}

main {
    width: 100%;
    justify-content: center;
}

.output,
.container {
    width: 100%;
    height: 200px;
    padding: 20px; 
    display: flex;
    flex-flow: row wrap;
    justify-content: center;
    align-items: center;
}

.btn {
    width: 150px;
    height: 150px;
    border-radius: 50%;
    background: rgb(255,0,101);
    background: radial-gradient(circle, rgb(255, 0, 64) 50%, rgba(121,9,9,1) 90%, rgba(2,0,36,1) 100%);
    border: solid 10px firebrick;
    cursor: pointer;
    font-weight: 600;
    font-size: 22px;
}

.btn:active,
.btn:hover {
    background: rgb(255,0,101);
    background: radial-gradient(circle, rgb(255, 0, 64) 30%, rgba(121,9,9,1) 80%, rgba(2,0,36,1) 100%);
    border: solid 10px firebrick;
}

.btn:focus {
    outline: none;
}