CSS3:box
box
CSS3:ボックス
CSS3:box-shadow
CSS3:box model
CSS3:border
https://developer.mozilla.org/en-US/docs/Learn/CSS/Building_blocks/The_box_model
CSS3-term.icon
https://img.shields.io/badge/CSS3-box-1572B6.svg?logo=css3&style=for-the-badge