The larger check works well in the headerbar, but not inline in various UI elements. This reverts the larger check since the latter is more common. For selection mode, a separate larger icon (selection-mode-symbolic) has been added to adwaita-icon-theme.
<?xml version="1.0" encoding="UTF-8"?>
<svg height="16px" viewBox="0 0 16 16" width="16px" xmlns="http://www.w3.org/2000/svg">
- <path d="m 15 3.484375 l -1 -1 l -7.46875 7.515625 l -3.414062 -3.476562 l -2 2 l 5.414062 5.476562 l 9.46875 -9.515625 z m 0 0" fill="#2e3436"/>
+ <path d="m 12.46875 3.484375 l -5.46875 5.515625 l -2.414062 -2.476562 l -2 2 l 4.414062 4.476562 l 7.46875 -7.515625 z m 0 0" fill="#2e3436"/>
</svg>