CSS中 @media screen 和@media only screen 和@media 的不同

@media screen and (max-width:632px)

This one is saying for a device with a screen and a window with max-width of 632px apply the style. This is almost identical to the above except you are specifying screen as opposed to the other available media types the most common other one being print.

@media (max-width:632px)

This one is saying for a window with a max-width of 632px that you want to apply these styles. At that size you would be talking about anything smaller than a desktop screen in most cases.

@media only screen and (max-width:632px)

The keyword ‘only’ can also be used to hide style sheets from older user agents. User agents must process media queries starting with ‘only’ as if the ‘only’ keyword was not present.