/usr/share/javascript/yui3/widget-buttons/assets/ is in libjs-yui3-common 3.5.1-1ubuntu3.
This file is owned by root:root, with mode 0o755.
..
/usr/share/javascript/yui3/widget-buttons/assets/skins/
/usr/share/javascript/yui3/widget-buttons/assets/skins/night/
/usr/share/javascript/yui3/widget-buttons/assets/skins/night/sprite_icons.gif
/usr/share/javascript/yui3/widget-buttons/assets/skins/night/widget-buttons-skin.css
/usr/share/javascript/yui3/widget-buttons/assets/skins/night/widget-buttons.css
/usr/share/javascript/yui3/widget-buttons/assets/skins/sam/
/usr/share/javascript/yui3/widget-buttons/assets/skins/sam/sprite_icons.gif
/usr/share/javascript/yui3/widget-buttons/assets/skins/sam/widget-buttons-skin.css
/usr/share/javascript/yui3/widget-buttons/assets/skins/sam/widget-buttons.css
/usr/share/javascript/yui3/widget-buttons/assets/widget-buttons-core.css