Added lark.js, manifest.json and .gitignore.

.gitignore

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+web-ext-artifacts/

lark.js

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+function RGBToRelLum(r,g,b) {
+   r = r / 255
+   g = g / 255
+   b = b / 255
+   if (r <= 0.03928){
+       r = r / 12.92
+   }
+   else {
+       r = ((r + 0.055) / 1.055) ** 2.4
+   }
+   if (r <= 0.03928){
+       r = r / 12.92
+   }
+   else {
+       r = ((r + 0.055) / 1.055) ** 2.4
+   }
+   if (r <= 0.03928){
+       r = r / 12.92
+   }
+   else {
+       r = ((r + 0.055) / 1.055) ** 2.4
+   }
+   var lum = 0.2126 * r + 0.7152 * g + 0.0722 * b
+   return lum
+}
+
+
+function contrastRatio(l1, l2) {
+    if (l1 > l2) {
+        return (l1 + 0.05) / (l2 + 0.05)
+    }
+    else {
+        return (l2 + 0.05) / (l1 + 0.05)
+    }
+}
+
+
+function rgb(r, g, b) {
+    return [r, g, b]
+}
+
+const blackLum = 0
+const black = '#000000';
+const whiteLum = 1
+const white = '#FFFFFF';
+var elements = document.querySelectorAll('input[type="password"], input[type="text"], input[type="email"], input[type="number"]')
+for (i = 0; i < elements.length ; i++) {
+   var bg = getComputedStyle(elements[i]).backgroundColor
+   var fg = getComputedStyle(elements[i]).color
+   var bgRGB = eval(bg)
+   var fgRGB = eval(fg)
+   var bgLum = RGBToRelLum(bgRGB[0], bgRGB[1], bgRGB[2])
+   var fgLum = RGBToRelLum(fgRGB[0], fgRGB[1], fgRGB[2])
+   var contrast = contrastRatio(bgLum, fgLum)
+   if (contrast < 4.5) {
+       var blackContrast = contrastRatio(fgLum, blackLum)
+       var whiteContrast = contrastRatio(fgLum, whiteLum)
+       if (blackContrast > whiteContrast) {
+           if (blackContrast >= 4.5) {
+               elements[i].style.backgroundColor = black;
+           }
+           else {
+               elements[i].style.backgroundColor = black;
+               elements[i].style.color = white;
+           }
+       }
+       else {
+           if (whiteContrast >= 4.5) {
+               elements[i].style.backgroundColor = white;
+           }
+           else {
+               elements[i].style.backgroundColor = black;
+               elements[i].style.color = white;
+           }
+       }
+   }
+}

manifest.json

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+{
+  "manifest_version": 2,
+  "name": "Lark",
+  "version": "1.0",
+  
+  "description": "Fixes input boxes on dark themes.",
+  
+  "content_scripts": [
+  {
+    "matches": ["<all_urls>"],
+    "js": ["lark.js"]
+  }
+  ],
+  "applications": {
+     "gecko": {
+        "id": "lark@webionite.com"
+     }
+  }
+}