ID>CLASS>LABLE

1em === recently?pounds of word, its parient??is the?closest html attribute

rem : root em

a good default font size:?

0.875em === 14px

border?： default box-sizing?= content-box， it will just set w and h of?content-box , the box model will not change. if set box-sizing = border-box, you can change height and width.

background :

????????background-image

????????background-position

????????background-size

????????background-repeat

????????background-origin

????????background-clip

????????background-attachment

of course background-color

The function :?linear-gradient()

????????

The linear-gradient function have three parameters that angle, start-color, end-color.

the angle, you can choose diferent parameters, such as to bottom right, to bottom, to top.

If you want to have a "color stop", you can directly add it to mid node:?

????????linear-gradient?(to right, red 0%, white 50%, blue 100%)

function:?repeat-linear-gradient()

box-shadow()

????????box-shadow can give element?box a shadow mode,?

????????text-shadow can give text a shadow mode

1em means "move number" horizontal direction first，vertical direction two step

if "move number" all are 0 , the shadow will be?showed?beneath? the element.

black is shadow color.

at the default situation, shadow and element size is completely same. if the element have a radius angle, the shadow too.

3d effect

:active{?}