1. The name of CSS is Cascading Style Sheet, which has the characteristic that properties defined later overwrite previously defined properties.
2.

The color attribute disappears, that is, no color attribute appears anymore?

颜色属性消失是什么意思, are you trying to make color invisible?
Or do you want .text_color的颜色 to inherit the color attributes of its parent?
Or make its color transparent (the element will not be visible)?

The former can only be achieved through javascript code, such as http://www.w3school.com.cn/jquery/jquery_ref_attributes.asp or http://www.w3school.com.cn/jsref/dom_obj_attributes.asp;
The latter can be inherited from the parent by setting color:inherit Properties,
To achieve the transparency effect, you can use the color:transparent attribute

If you no longer need to display the text in the element, you can hide it or use negative indentation; and in the later introduction, set the text color to a transparent color color: transparent;, as in the following example:

http://jsfiddle.net/65PLY/1/

Inherit

css.text_color{
    color:inherit;
}

Transparent

css.text_color{
    color:transparent;
}

Flush out (#box has a p id of text_color, it can be flushed out no matter where it is)

css#box p.text_color{
    color:red;
}