Extend last li to remaining width of a ul?

Question

I have been puzzled about this for a while now. Here is what i have now:

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Answer 1

You can float all elements but the last to the left.

The last element's box model will then extend behind these floated list items (even though the content doesn't). overflow:hidden will prevent this behaviour; the box model will begin when the last floated item ends, as if the floated items were still in the natural flow of the page.

ul, li{
    margin:0;
    padding:0;
    
    list-style-type:none;
}

ul li{
    display: block;
    float:left;
}

ul li:last-child{
    background-color: #ffffd;

    float:none;
    overflow:hidden;
}

<ul>
    <li>Item</li>
    <li>Item</li>
    <li>I will extend to the end of the page.. No matter how far. I will also not drop beneath my previous items, even if the text in here requires me to span over multiple lines.</li>    
</ul>

An edit of your newly added JSFiddle:

JSFiddle

Answer 2

ul>li:last-of-type {width:whatever}

So the two li's before the last would float:left and have 20% on both and the last one can have 60%;

Also don't forgot to clear the flaots with

ul {overflow:auto;}

and keep the % perfect so the borders do not escape:

ul>li {box-sizing:border-box;}