A half-course Summary of CSS Learning (questions to consider when learning CSS)

What should be kept in mind when using CSS?
We have summarized the following points. If there is a new one, add it again (:

1.Cross-browserCross-browser (I personally think this is the most important issue ). I have a book titled website reconstruction.
2. Different CSS files should be selected for different positions to display different effects.Media: Screen, print or other.
Because the display is different from the position, the required CSS file may be very different, otherwise it will affect the effect.
3. User'sBrowser backgroundNot all are set to white. Many people may ignore this detail and do not consider the background color when defining the body first,
It is assumed that the browser background of the client must be white.
4. Do not use (background) images to display important information, because in some network conditions, images may not be displayed, or you have set images on the client.
Do not show, this will affect the effect of the website. (The background image is a modifier rather than a "content ").
5. The access convenience of different visitors needs to be considered. For example, users may be blind or deaf-mute. In this way, some colors or sounds cannot be used as carriers or other functions that reflect the content of the website. (The text is king and the content is king. Therefore, the website should be mainly reflected in words)