Centering an icon in SVG - html

Question

I have the following very simple SVG:
<div id="circli" class="svg-container">
<svg xmlns="http://www.w3.org/2000/svg" version="1.1" viewBox="0 0 194 186" class="circliful">
<g stroke="#ccc">
<line x1="133" y1="50" x2="140" y2="40" stroke-width="2"></line>
</g>
<g stroke="#ccc">
<line x1="140" y1="40" x2="200" y2="40" stroke-width="2"></line>
</g>
<circle cx="100" cy="100" r="57" class="border" fill="#eee" stroke="none" stroke-width="15" stroke-dasharray="360" transform="rotate(-90,100,100)"></circle>
<circle class="circle" cx="100" cy="100" r="57" fill="none" stroke="#3498DB" stroke-width="5" stroke-dasharray="180, 20000" transform="rotate(-90,100,100)"></circle>
<text text-anchor="middle" x="100" y="110" class="icon" style="font-size: 40px" fill="#3498DB"></text>
<text class="timer" text-anchor="middle" x="175" y="35" style="font-size: 22px; undefined;" fill="#aaa">50%</text>
</svg>
</div>
My question is pertaining to the icon and how it is being centered, I am not quite understanding the logic behind how exactly the author of this code has centered the icon. The code for the icon and the circle looks like below:
<circle cx="100" cy="100" r="57" class="border" fill="#eee" stroke="none" stroke-width="15" stroke-dasharray="360" transform="rotate(-90,100,100)"></circle>
<circle class="circle" cx="100" cy="100" r="57" fill="none" stroke="#3498DB" stroke-width="5" stroke-dasharray="180, 20000" transform="rotate(-90,100,100)"></circle>
<text text-anchor="middle" x="100" y="110" class="icon" style="font-size: 40px" fill="#3498DB"></text>
Notice the x, y attributes on the <text> element like so:
x="100" y="110"
Now if you play around in the console, you'll notice that any value apart from that will make the icon no longer centered.
I am not quite understanding the logic for centering the icon here. Can anybody explain please?
P.S. I believe the y value is 110 to counter the size of the icon, something like negative margin when vertically aligning a absolutely positioned element.
FIDDLE HERE Can somebody please explain this to me?

Answer 1

The icon is centered due to two attribute-value pairs:
It is horizontally centered because of the text-anchor = 'middle' attribute. When text anchor is set to middle, the text is positioned such that the center of the text is placed at the x coord that was given as attribute for the text tag. Below is what MDN says about this property-value pair.
middle
The rendered characters are aligned such that the middle of the text string is at the current text position. (For text on a path, conceptually the text string is first laid out in a straight line. The midpoint between the start of the text string and the end of the text string is determined. Then, the text string is mapped onto the path with this midpoint placed at the current text position.)
Here the circle is created such that its center is at (100,100) and hence setting the text x='100' and setting text-anchor = 'middle' positions the text at the horizontal center of the circle.
It is vertically centered because of the y attribute's value. This involves trial and error based on the font-size and the font of the text. In this particular case, the font-size: 40px means that the height of the box is roughly 26 units. This means that setting y = '113' will actually be setting the text at vertical middle (to be precise). The value of y = '100' doesn't put it at exact center.
In the below snippet we can see how the font-size impacts the value of y attribute. Basically the value for y should be set in such a way that half the text will be above the center the rest will be below the center. So, y is roughly center point + (height of text / 2).
As explained by Lea Verou in this article, there is a property called dominant-baseline: middle; which will center text vertically without the need for such calculations but the browser support is poor.
.svg-container {
max-width:200px;
}
<div id="circli" class="svg-container">
<svg xmlns="http://www.w3.org/2000/svg" version="1.1" viewBox="0 0 194 186" class="circliful">
<g stroke="#ccc">
<line x1="133" y1="50" x2="140" y2="40" stroke-width="2"></line>
</g>
<g stroke="#ccc">
<line x1="140" y1="40" x2="200" y2="40" stroke-width="2"></line>
</g>
<circle cx="100" cy="100" r="57" class="border" fill="#eee" stroke="none" stroke-width="15" stroke-dasharray="360" transform="rotate(-90,100,100)"></circle>
<circle class="circle" cx="100" cy="100" r="57" fill="none" stroke="#3498DB" stroke-width="5" stroke-dasharray="180, 20000" transform="rotate(-90,100,100)"></circle>
<text text-anchor="middle" x="100" y="113" class="icon" style="font-size: 40px" fill="#3498DB"></text>
<text class="timer" text-anchor="middle" x="175" y="35" style="font-size: 22px; undefined;" fill="#aaa">50%</text>
</svg>
</div>
<div id="circlj" class="svg-container">
<svg xmlns="http://www.w3.org/2000/svg" version="1.1" viewBox="0 0 194 186" class="circliful">
<g stroke="#ccc">
<line x1="133" y1="50" x2="140" y2="40" stroke-width="2"></line>
</g>
<g stroke="#ccc">
<line x1="140" y1="40" x2="200" y2="40" stroke-width="2"></line>
</g>
<circle cx="100" cy="100" r="57" class="border" fill="#eee" stroke="none" stroke-width="15" stroke-dasharray="360" transform="rotate(-90,100,100)"></circle>
<circle class="circle" cx="100" cy="100" r="57" fill="none" stroke="#3498DB" stroke-width="5" stroke-dasharray="180, 20000" transform="rotate(-90,100,100)"></circle>
<text text-anchor="middle" x="100" y="109.5" class="icon" style="font-size: 30px;" fill="#3498DB"></text>
<text class="timer" text-anchor="middle" x="175" y="35" style="font-size: 22px; undefined;" fill="#aaa">50%</text>
</svg>
</div>