feat: add content to empty catalogs

src/theme/util/_mixins.scss

@@ -1,5 +1,5 @@
 /*!
- * Copyright (C) 2022 StApps
+ * Copyright (C) 2023 StApps
  * This program is free software: you can redistribute it and/or modify it
  * under the terms of the GNU General Public License as published by the Free
  * Software Foundation, version 3.
@@ -22,36 +22,43 @@
     @content;
   }
 }
+
 @mixin ion-sm-down {
   @media (max-width: 575.98px) {
     @content;
   }
 }
+
 @mixin ion-md-up {
   @media (min-width: 768px) {
     @content;
   }
 }
+
 @mixin ion-md-down {
   @media (max-width: 767.98px) {
     @content;
   }
 }
+
 @mixin ion-lg-up {
   @media (min-width: 992px) {
     @content;
   }
 }
+
 @mixin ion-lg-down {
   @media (max-width: 991.98px) {
     @content;
   }
 }
+
 @mixin ion-xl-up {
   @media (min-width: 1200px) {
     @content;
   }
 }
+
 @mixin ion-xl-down {
   @media (max-width: 1199.98px) {
     @content;
@@ -83,3 +90,9 @@
   // and disregard border radius in some cases
   transform: translateZ(0);
 }
+
+@mixin content-padding {
+  margin-inline-start: calc(
+    clamp(0px, (100% - var(--preferred-content-width)) / 2, var(--content-inline-start-padding-bias))
+  );
+}