Features I added:
* Animated buttons on hover and click, also changes cursor * Clearing of old calculated totals/grades and mean/average when changing input * Prevention of any input other than positive integers - hidden spin buttons - red box shadow if invalid input - allowed one decimal place for half marks - two decimals is invalid input - use of min/max properties * A warning message when trying to calculate average/mean with blank inputs present (took a while to figure out proper inline-block setup) - animates fading in and fading out of warning message when a button is pressed and all inputs are valid - warning message flashes if already visible and button is pressed with invalid inputs present (css animation) * A letter grade column to show what letter grade a given percentage on an assignment would yield * Whole page remains same size without weird scaling issues when dragging window size (purpose of #casing div)