The cells example would be improved by keeping the top left corner clear by making that cell stick in place and on top: #colHeadings .rowHeading { z-inde

The cells example would be improved by keeping the top left corner clear by making that cell stick in place and on top: #colHeadings .rowHeading { z-index: 3; top: 0; } I also believe keyboard navigability is essential for the cells example, although the task specification neglected to mention it. (But then, the spec doesn’t specify anything about the formulas either—though it does include a picture depicting something like =SUM(B1:C4).) Tab and Shift+Tab work to shift cell focus, but that’s all; at the very least, Up/Down/Left/Right should work for cell navigation, and some way of entering edit mode without needing the mouse (start with F2, which is standard across spreadsheet apps that I know; perhaps Enter too, though they don’t).