How to inherit the contents of an existing class? _html/css_WEB-ITnose

In this case, b has background-color and colo at the same time...
Me I hope to use b to inherit all the attributes of a, and modify or supplement other attributes. The premise is that a is not changed, and b does not exist when a is declared, so this cannot be solved.

You can write three styles, .a {color:red;//a unique style} .b {color:blue;//bunique style} .a,.b {background-color :red;//a b public style}
I want a to be the default style and b to be a selected style, so a cannot be declared together with b, and there cannot be a common style.

adasd

Yours, Is this what you mean?

adasd

Yours, Is this what you mean?
That’s it, that’s how I use it now, but I hope that I can use the function of a b with only b, but I don’t want to write the code twice

There seems to be no solution? If you can’t help it, just post it and share the hard work with everyone