縦方向の中央揃えとかできて便利そう https://www.w3schools.com/css/css3_flexbox.asp A Complete Guide to Flexbox | CSS-Tricks 絵で眺める CSS Flexbox CSS Flexible Box Layout - CSS: Cascading Style Sheets | MDN flex-basis - CSS: Cascading Style Sheets | MDN flex-grow - CSS: Cascading Style Sheets | MDN flex-shrink - CSS: Cascading Style Sheets | MDN