how is it possible to make one class inherit from another in the CSS file?

```
input.btn {
    border:1px solid #23458c;
    background:url('gfx/layout.btn_bg.png');
    color:#f0f5fa;
    font-weight:bold;
    margin-right:6px;
    padding:1px 6px 2px 6px;
    cursor:pointer;
}

input.btn_light {
    border:1px solid #717b8f;
    background:url('gfx/layout.btn_light_bg.png');
}

```

here I want `input.btn_light` to inherit from `input.btn`.. how is that possible to do in the CSS file?

@vadiklk
--------

```
input.btn {
    border:1px solid #23458c;
    background:url('gfx/layout.btn_bg.png');
    color:#f0f5fa;
    font-weight:bold;
    margin-right:6px;
    padding:3px 6px 4px 6px;
    cursor:pointer;
}

input.btn_light {
    input.btn;
    border:1px solid #717b8f;
    background:url('gfx/layout.btn_light_bg.png');
}

```