一、
px：
One pixel. For screen displays, it traditionally represents one device pixel (dot). However, for printers and high-resolution screens, one CSS pixel implies multiple device pixels. 1px = 1/96th of 1in.
em：
Represents the calculated font-size of the element. If used on the font-size property itself, it represents the inherited font-size of the element.
rem：
Represents the font-size of the root element (typically <html>). When used within the root element font-size, it represents its initial value (a common browser default is 16px, but user-defined preferences may modify this).
fr：
Tracks can be defined using any length unit. Grid also introduces an additional length unit to help us create flexible grid tracks. The new fr unit represents a fraction of the available space in the grid container. The next grid definition would create three equal width tracks that grow and shrink according to the available space.
二、
颜色表示法：
/* Keyword values */ color: currentcolor; /* <named-color> values */ color: red; color: orange; color: tan; color: rebeccapurple; /* <hex-color> values */ color: #090; color: #009900; color: #090a; color: #009900aa; /* <rgb()> values */ color: rgb(34, 12, 64, 0.6); color: rgba(34, 12, 64, 0.6); color: rgb(34 12 64 / 0.6); color: rgba(34 12 64 / 0.3); color: rgb(34.0 12 64 / 60%); color: rgba(34.6 12 64 / 30%); /* <hsl()> values */ color: hsl(30, 100%, 50%, 0.6); color: hsla(30, 100%, 50%, 0.6); color: hsl(30 100% 50% / 0.6); color: hsla(30 100% 50% / 0.6); color: hsl(30.0 100% 50% / 60%); color: hsla(30.2 100% 50% / 60%); /* Global values */ color: inherit; color: initial; color: unset;
颜色表：
