Subscribe topic button style fixes

src/components/Author/Card.module.scss

@@ -305,5 +305,5 @@
 }
 
 .isSubscribing {
-  color: transparent;
+  opacity: 0.5;
 }

src/components/Topic/Card.module.scss

@@ -118,9 +118,10 @@
 }
 
 .isSubscribing {
-  color: transparent;
+  opacity: 0.5;
 }
 
 .isSubscribed {
   background: #000;
+  color: #fff;
 }

src/styles/app.scss

@@ -187,6 +187,11 @@ button {
   cursor: pointer;
   font-family: inherit;
   padding: 0;
+
+  &[disabled] {
+    cursor: default;
+    opacity: 0.5 !important;
+  }
 }
 
 .button {
@@ -253,6 +258,11 @@ button {
     color: #fff;
     opacity: 1;
   }
+
+  &[disabled]:hover {
+    background: #fff;
+    color: #000;
+  }
 }
 
 .button--content-index {
@@ -710,7 +720,9 @@ astro-island {
 .mode-switcher {
   @include font-size(1.5rem);
 
-  text-align: right;
+  @include media-breakpoint-up(md) {
+    text-align: right;
+  }
 }
 
 .mode-switcher__control {