body{font-size: 12px;} /* 1 em = 12px */
#box1{font: 12px/22px Arial, Helvetica, sans-serif bold;}
/* 12px/22px 表示 font size 12px, line height 22px. */
#box2{font: 1.5em/1.5em Arial, Helvetica, sans-serif bold;}
/* 1.5em/1.5em 表示 font size 18px, line height 27px. */
