Unexpected cssTailwind behavior

Question

I pass this simple tailwind css code:

    <div class="grid grid-cols-12 w-full">
        
        <div class="col-span-1 w-full bg-orange-300">uuuu</div>

            <div class="flex flex-row justify-end items-center col-span-10 bg-gray-200">

            </div>

        <div class="col-span-1 w-full bg-orange-300">uuuu</div>

    </div>  

</div>

When, in the central div I put col-span-9, it occupies 9 cells, which with the first one cover 10 using 1 cell plus the last div and leaving a cell left; If I put col-span-10 in the central div, instead of completing the cells, it collapses, occupying only one cell; Let me tell you that there are no side margins or padding. It should occupy all 10 cells, leaving the whole symmetrical, but there is no solution. Could someone help me with this??. Thank you.

I hope you explain to me if you see any mistakes, and understand what the mistake is.