style: style and visibility fixes for remove favourites button

Relates #119

src/components/PopupCard/PopupCard.css

@@ -22,9 +22,37 @@
   border: 2px solid var(--highlight);
 }
 
-.popup-card--remove-button {
-  color: var(--base);
+.close-button--container {
   position: absolute;
+  background-color: rgba(96, 96, 96, 0.6);
+  padding: 3px;
   top: 10px;
   right: 10px;
+  z-index: 1;
+  border-radius: 7px;
+}
+
+.popup-card--remove-button {
+  color: var(--base);
+  background-color: var(--base);
+  display: flex;
+  justify-content: center;
+  align-items: center;
+  height: 20px;
+  width: 20px;
+  z-index: 2;
+  clip-path: polygon(
+    20% 0%,
+    0% 20%,
+    30% 50%,
+    0% 80%,
+    20% 100%,
+    50% 70%,
+    80% 100%,
+    100% 80%,
+    70% 50%,
+    100% 20%,
+    80% 0%,
+    50% 30%
+  );
 }