Keep the middle item centered when side items have different widths

Question

Imagine the following layout, where the dots represent the space between the boxes:

[Left box]......[Center box]......[Right box]

Answer 1

you can also use this simple way to reach exact center alignment for middle element :

.container {
    display: flex;
    justify-content: space-between;
}

.container .sibling {
    display: flex;
    align-items: center;
    height: 50px;
    background-color: gray;
}

.container .sibling:first-child {
    width: 50%;
    display: flex;
    justify-content: space-between;
}

.container .sibling:last-child {
    justify-content: flex-end;
    width: 50%;
    box-sizing: border-box;
    padding-left: 100px; /* .center's width divided by 2 */
}

.container .sibling:last-child .content {
    text-align: right;
}

.container .sibling .center {
    height: 100%;
    width: 200px;
    background-color: lightgreen;
    transform: translateX(50%);
}

codepen: https://codepen.io/ErAz7/pen/mdeBKLG