Fix close button to be semantic html

Author: kdoroszewicz

src/toastify-es.js

@@ -238,10 +238,11 @@ class Toastify {
       // Adding a close icon to the toast
       if (this.options.close === true) {
         // Create a span for close element
-        let closeElement = document.createElement("span");
-        closeElement.innerHTML = "✖";
-
+        let closeElement = document.createElement("button");
+        closeElement.type = "button";
+        closeElement.setAttribute("aria-label", "Close");
         closeElement.className = "toast-close";
+        closeElement.innerHTML = "✖";
 
         // Triggering the removal of toast from DOM on close click
         closeElement.addEventListener(

src/toastify.css

@@ -28,6 +28,12 @@
 }
 
 .toast-close {
+    background: transparent;
+    border: 0;
+    color: white;
+    cursor: pointer;
+    font-family: inherit;
+    font-size: 1em;
     opacity: 0.4;
     padding: 0 5px;
 }

src/toastify.js

@@ -160,10 +160,11 @@
       // Adding a close icon to the toast
       if (this.options.close === true) {
         // Create a span for close element
-        var closeElement = document.createElement("span");
-        closeElement.innerHTML = "✖";
-
+        var closeElement = document.createElement("button");
+        closeElement.type = "button";
+        closeElement.setAttribute("aria-label", "Close");
         closeElement.className = "toast-close";
+        closeElement.innerHTML = "✖";
 
         // Triggering the removal of toast from DOM on close click
         closeElement.addEventListener(