paste this into Javascript console to see what fonts are being used

whatthefont.js

function walk(node) {
  // I stole this function from here:
  // http://is.gd/mwZp7E

  var child, next;

  var tagName = node.tagName ? node.tagName.toLowerCase() : "";
  if (tagName == 'input' || tagName == 'textarea') {
    return;
  }
  if (node.classList && node.classList.contains('ace_editor')) {
    return;
  }

  switch (node.nodeType) {
    case 1: // Element
    case 9: // Document
    case 11: // Document fragment
      child = node.firstChild;
      while (child) {
        next = child.nextSibling;
        walk(child);
        child = next;
      }
      break;

    case 3: // Text node
      handleText(node);
      break;
  }
}

function handleText(textNode) {
  var v = textNode.nodeValue;
  var cs = window.getComputedStyle(textNode.parentNode)
  if (cs && textNode.parentNode.nodeName != "STYLE" && textNode.parentNode.nodeName != "SCRIPT") {
    let font = cs.fontFamily || ""
    let size = cs.fontSize
    let weight = cs.fontWeight
    let weights = {
      100: "Thin",
      200: "Extra Light",
      300: "Light",
      400: "Regular",
      500: "Medium",
      600: "Semibold",
      700: "Bold",
      800: "Extra Bold",
      900: "Black"
    }



    font = font.replace("sans-serif", "").replace(/[,"]/g, "").trim()
    font = font.replace("Red Hat Text", "RHT").replace("Red Hat Display", "RHD")
    textNode.nodeValue = font + " " + size + " " + weights[weight]
  }
}
walk(document.body)

You may want to consider using TreeWalker to find textNodes; it's significantly faster, especially for large DOM's. An example is below, written as a DevTools snippet (though you can paste it on the console for use as well).

Note, this won't travel the ShadowDOM (which we don't have a great story for yet on the platform, but it is being discussed).

function findTextNodesFor(element){
  let node; 
  const discoveredTextNodes = []; 
  const walkTree = document.createTreeWalker(element, NodeFilter.SHOW_TEXT, null, false);
  while(node = walkTree.nextNode()) {
    discoveredTextNodes.push(node);
  }
  return discoveredTextNodes;
}

weights = {
  100: "Thin",
  200: "Extra Light",
  300: "Light",
  400: "Regular",
  500: "Medium",
  600: "Semibold",
  700: "Bold",
  800: "Extra Bold",
  900: "Black"
};

findTextNodesFor(document.body)
  .filter(node => !['SCRIPT', 'STYLE', 'NOSCRIPT'].includes(node.parentNode.nodeName))
  .forEach(node => {
  const computedStyle = window.getComputedStyle(node.parentNode);
  let font = computedStyle.fontFamily || "";
  const size = computedStyle.fontSize;
  const weight = computedStyle.fontWeight;

  font = font.replace("sans-serif", "").replace(/[,"]/g, "").trim();
  font = font.replace("Red Hat Text", "RHT").replace("Red Hat Display", "RHD");
  node.nodeValue = font + " " + size + " " + weights[weight];
});

Similarly, if you just wanted a look at the styles you have defined, you could do so using new Set() for storing unique values, which can be useful for quick reports:

function findTextNodesFor(element){
  let node; 
  const discoveredTextNodes = []; 
  const walkTree = document.createTreeWalker(element, NodeFilter.SHOW_TEXT, null, false);
  while(node = walkTree.nextNode()) {
    discoveredTextNodes.push(node);
  }
  return discoveredTextNodes;
}

weights = {
  100: "Thin",
  200: "Extra Light",
  300: "Light",
  400: "Regular",
  500: "Medium",
  600: "Semibold",
  700: "Bold",
  800: "Extra Bold",
  900: "Black"
};

fonts = new Set();

findTextNodesFor(document.body)
  .filter(node => !['SCRIPT', 'STYLE', 'NOSCRIPT'].includes(node.parentNode.nodeName))
  .forEach(node => {
  const computedStyle = window.getComputedStyle(node.parentNode);
  const font = computedStyle.fontFamily || "";
  const size = computedStyle.fontSize;
  const weight = computedStyle.fontWeight;
  fonts.add(`${size} ${weights[weight]} ${font}`);
});

console.log(fonts);