font-**(font-weight系) クラスの見本

font-thin
= font-weight: 100;
font-extralight
= font-weight: 200;
font-light
= font-weight: 300;
font-normal
= font-weight: 400;
font-medium
= font-weight: 500;
font-semibold
= font-weight: 600;
font-bold
= font-weight: 700;
font-extrabold
= font-weight: 800;
font-black
= font-weight: 900;