Centering SVGs in a grid cell

Question

I see how one can position an item inside a grid cell such that it appears in any of the four corners. To summarize, the cell itself receives the styling position: relative;, and each of the items gets styled as position: absolute;, top: 0;, and left: 0;, replacing top and left as appropriate.

Here I'd like to style three SVG images at the center left, center-center, and the center-right of a grid cell.

Using the following three stylings

/* center left */
vertical-align: middle;
left: 0;

/* center-center */
text-align: center;
vertical-align: middle;

/* center right */
vertical-align: middle;
right: 0;

is ineffective. Why?

body { margin: 40px; }
.header {
    grid-area: header;
    height: 100px;
    position: relative;
    background-color: #999;
}
.content {
    grid-area: content;
    height: 200px;
}
.wrapper {
    display: grid;
    grid-gap: 10px;
    grid-template-columns: 800px;
    grid-template-areas:
        "header"
        "content";
    background-color: #fff;
    color: #444;
}
.box {
    background-color: #444;
    color: #fff;
    border-radius: 5px;
    padding: 50px;
    font-size: 150%;
}

.centerleft {
    vertical-align: middle;
    left: 0;
}
.centercenter {
    text-align: center;
    vertical-align: middle;
}
.centerright {
    vertical-align: middle;
    right: 0;
}
.circle {
    height: 50px;
    stroke: black; fill: cyan;
}

<div class="wrapper">
    <div class="box header">
        <svg xmlns="http://www.w3.org/2000/svg"
            class="centerleft circle"
            viewBox="0 0 100 100">
            <circle class="mycircle" cx="50" cy="50" r="45"/>
        </svg>
        <svg xmlns="http://www.w3.org/2000/svg"
            class="centercenter circle"
            viewBox="0 0 100 100">
            <circle class="mycircle" cx="50" cy="50" r="45"/>
        </svg>
        <svg xmlns="http://www.w3.org/2000/svg"
            class="centerright circle"
            viewBox="0 0 100 100">
            <circle class="mycircle" cx="50" cy="50" r="45"/>
        </svg>
    </div>
    <div class="box content">
        Content
    </div>
</div>

Since the same cell has three items with different stylings, variations on

grid-item {
    display: flex;
    align-items: center;
    justify-content: center;
}

as described here did not help.

Answer 1

This can be easily achieved by using flex. Added style to box selector

body { margin: 40px; }
.header {
    grid-area: header;
    height: 100px;
    position: relative;
    background-color: #999;
}
.content {
    grid-area: content;
    height: 200px;
}
.wrapper {
    display: grid;
    grid-gap: 10px;
    grid-template-columns: 800px;
    grid-template-areas:
        "header"
        "content";
    background-color: #fff;
    color: #444;
}
.box {
    background-color: #444;
    color: #fff;
    border-radius: 5px;
    padding: 50px;
    font-size: 150%;
    display: flex;
    display: -webkit-flex;
    justify-content: space-between;
    -webkit-justify-content: space-between;
}

.centerleft {
    vertical-align: middle;
    left: 0;
}
.centercenter {
    text-align: center;
    vertical-align: middle;
}
.centerright {
    vertical-align: middle;
    right: 0;
}
.circle {
    height: 50px;
    stroke: black; fill: cyan;
}

<div class="wrapper">
    <div class="box header">
        <svg xmlns="http://www.w3.org/2000/svg"
            class="centerleft circle"
            viewBox="0 0 100 100">
            <circle class="mycircle" cx="50" cy="50" r="45"/>
        </svg>
        <svg xmlns="http://www.w3.org/2000/svg"
            class="centercenter circle"
            viewBox="0 0 100 100">
            <circle class="mycircle" cx="50" cy="50" r="45"/>
        </svg>
        <svg xmlns="http://www.w3.org/2000/svg"
            class="centerright circle"
            viewBox="0 0 100 100">
            <circle class="mycircle" cx="50" cy="50" r="45"/>
        </svg>
    </div>
    <div class="box content">
        Content
    </div>
</div>