// the <path> is basically a shorter version of a <rect>
$svg = <<<SVG
-<svg xmlns="http://www.w3.org/2000/svg" width="16" height="16"><path fill="#{$backgroundColor}" d="M0 0h16v16H0z"/><text x="8" y="8" fill="#{$textColor}" text-anchor="middle" dy=".3em" font-family="Arial" font-size="7">{$text}</text></svg>
+<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 16 16" width="16" height="16"><path fill="#{$backgroundColor}" d="M0 0h16v16H0z"/><text x="8" y="8" fill="#{$textColor}" text-anchor="middle" dy=".3em" font-family="Arial" font-size="7">{$text}</text></svg>
SVG;
$this->src = "data:image/svg+xml;base64," . base64_encode($svg);