fix size of toggle icon, make container square

core/img/actions/toggle.svg

 <?xml version="1.0" encoding="UTF-8" standalone="no"?>
-<svg xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#" xmlns="http://www.w3.org/2000/svg" xml:space="preserve" height="9px" viewBox="0 0 16 9" width="16px" version="1.1" y="0px" x="0px" xmlns:cc="http://creativecommons.org/ns#" enable-background="new 0 0 16 9" overflow="visible" xmlns:dc="http://purl.org/dc/elements/1.1/">
-<path d="m7.999 0c-3.109 0-5.926 1.719-7.999 4.5 2.073 2.781 4.89 4.5 7.999 4.5 3.111 0 5.928-1.719 8.001-4.5-2.073-2.781-4.892-4.5-8.001-4.5zm0.001 7.5c-1.657 0-3-1.343-3-3s1.343-3 3-3c1.657 0 3 1.343 3 3s-1.343 3-3 3z" fill="#222"/>
-<circle cy="4.501" cx="8" r="1.5" fill="#222"/>
-</svg>
+<svg xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#" xmlns="http://www.w3.org/2000/svg" enable-background="new 0 0 16 9" xml:space="preserve" overflow="visible" height="16" width="16" version="1.1" y="0px" x="0px" xmlns:cc="http://creativecommons.org/ns#" xmlns:dc="http://purl.org/dc/elements/1.1/" viewBox="0 0 16 16"><path fill="#222" d="m8 3c-3.109 0-5.927 1.719-8 4.5 2.073 2.781 4.891 4.5 8 4.5 3.111 0 5.927-1.719 8-4.5-2.073-2.781-4.891-4.5-8-4.5zm0 1.5c1.657 0 3 1.343 3 3s-1.343 3-3 3-3-1.343-3-3 1.343-3 3-3zm0 1.5c-0.8284 0-1.5 0.6716-1.5 1.5s0.6716 1.5 1.5 1.5 1.5-0.6716 1.5-1.5-0.6716-1.5-1.5-1.5z"/></svg>