body {
    background: white;
    overflow: hidden;
    display: block;
    justify-content: center;
    align-items: center;
}


.flex-container {
    display: flex;
}
.flex-child {
    flex: 1;
    border: 2px solid yellow;
}  
.flex-child:first-child {
    margin-right: 20px;
}