Support multiple values merge

[yisibl]

input:

h1 {
    border: 1px solid red;
    background-color: red;
    background-position: 50% 100%;
}

h1 {
    border: 1px #f00 solid;
    background-color: #f00;
    background-position: center bottom;
}

h1 {
    border: solid 1px rgb(255, 0, 0);
}

output:

h1 {
    border: 1px solid red;
    background-color: red;
    background-position: 50% 100%;
}

[chrisvfritz]

I believe this would be very undesirable, since fallback properties are sometimes used in CSS.