function toggleHTMLClassVisibility(className) {
	var x = document.getElementsByClassName(className);
	var i;
	for (i = 0; i < x.length; i++) {
		if (x[i].style.display === "none") {
			x[i].style.display = "block";
		} else {
			x[i].style.display = "none";
		}
	}
};

function toggleHistogramMarker() {
	toggleHTMLClassVisibility("histogram_marker");
};

function toggleGradingScheme() {
	toggleHTMLClassVisibility("grading_scheme");
};