css - inherit from another class

Question

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');
}

Answer 1

Give the HTML element both classes:

<input type="submit" class="btn btn_light" value="Action" />