* { box-sizing: border-box; }

body {
    margin: 0;
    background: #2C73D2;
    color: #fff;
    text-align: center;
}

.flex-container {
    border: 10px solid #F9F871;
    max-width: 600px;
    margin: 0 auto;
    padding: .25em;
}

.flex-item {
    background: #8BEE86;
    margin: .5em;
    padding: .5em;
    color: #424656;
}