Fix CORS and Mixed-Content issue & Bug Fixes

This fixes the following issues:
- Text selection color was incorrect
- The 'send again' button glitched on page load

This also adds some finishing touches to the proxy code (closes #199)
and that in turn resolves #175 and resolves #2

Finally, this adds the fonts to the application assets allowing
them to be cached by the service worker.

assets/css/themes.scss

@@ -8,7 +8,7 @@
  */
 
 // Dark is the default theme variant.
-:root {
+@mixin darkTheme {
   // Dark Background color
   --bg-dark-color: rgb(41, 42, 45);
   // Background color
@@ -25,11 +25,21 @@
   --err-color: rgb(41, 42, 45);
   // Acent color
   --ac-color: #50fa7b;
+  --ac-sel-color: rgb(80, 250, 123, 0.8);
   // Active text color
   --act-color: rgb(37, 38, 40);
 }
 
-:root.light {
+:root {
+  @include darkTheme;
+}
+@media(prefers-color-scheme: dark) {
+  :root.auto {
+    @include darkTheme;
+  }
+}
+
+@mixin lightTheme {
   // Dark Background color
   --bg-dark-color: #f6f6f6;
   // Background color
@@ -46,11 +56,21 @@
   --err-color: #f6f6f6;
   // Acent color
   --ac-color: #57b5f9;
+  --ac-sel-color: #57b5f9;
   // Active text color
   --act-color: #ffffff;
 }
 
-:root.black {
+:root.light {
+  @include lightTheme;
+}
+@media(prefers-color-scheme: light) {
+  :root.auto {
+    @include lightTheme;
+  }
+}
+
+@mixin blackTheme {
   // Dark Background color
   --bg-dark-color: rgb(8, 8, 8);
   // Background color
@@ -67,52 +87,10 @@
   --err-color: rgb(8, 8, 8);
   // Acent color
   --ac-color: #50fa7b;
+  --ac-sel-color: rgb(80, 250, 123, 0.8);
   // Active text color
   --act-color: #000000;
 }
-
-@media(prefers-color-scheme: light) {
-  :root.auto {
-    // Dark Background color
-    --bg-dark-color: #f6f6f6;
-    // Background color
-    --bg-color: #ffffff;
-    // Auto-complete color
-    --atc-color: #ebebeb;
-    // Text color
-    --fg-color: #525252;
-    // Light Text color
-    --fg-light-color: rgb(150, 155, 160);
-    // Border color
-    --brd-color: #eeeeed;
-    // Error color
-    --err-color: #f6f6f6;
-    // Acent color
-    --ac-color: #57b5f9;
-    // Active text color
-    --act-color: #ffffff;
-  }
-}
-
-@media(prefers-color-scheme: dark) {
-  :root.auto {
-    // Dark Background color
-    --bg-dark-color: rgb(41, 42, 45);
-    // Background color
-    --bg-color: rgb(37, 38, 40);
-    // Auto-complete color
-    --atc-color: rgb(49, 49, 55);
-    // Text color
-    --fg-color: rgb(247, 248, 248);
-    // Light Text color
-    --fg-light-color: rgb(150, 155, 160);
-    // Border color
-    --brd-color: rgb(48, 47, 55);
-    // Error color
-    --err-color: rgb(41, 42, 45);
-    // Acent color
-    --ac-color: #50fa7b;
-    // Active text color
-    --act-color: rgb(37, 38, 40);
-  }
+:root.black {
+  @include blackTheme;
 }