CSS: Fix handling of white background

src/pretix/static/pretixbase/scss/_theme_variables.scss

@@ -130,5 +130,14 @@ $in-border-radius-small: 2px !default;
     --pretix-info-icon: url("data:image/svg+xml,%3Csvg%20viewBox='0%200%2036%2036'%20xmlns='http://www.w3.org/2000/svg'%20xml:space='preserve'%3E%3Ccircle%20cx='18'%20cy='18'%20r='16'%20fill='%23fff'/%3E%3Cpath%20d='M21.74%2022.66a.7.7%200%200%200-.7-.7h-.7v-6.28a.7.7%200%200%200-.7-.7h-4.19a.7.7%200%200%200-.7.7v1.4c0%20.38.32.7.7.7h.7v4.19h-.7a.7.7%200%200%200-.7.7v1.4c0%20.37.32.7.7.7h5.6a.7.7%200%200%200%20.69-.7v-1.4Zm-1.4-12.57a.7.7%200%200%200-.7-.7h-2.8a.7.7%200%200%200-.69.7v2.1c0%20.38.32.7.7.7h2.8a.7.7%200%200%200%20.7-.7v-2.1Z'%20fill='#{url-friendly-colour(darken($in-brand-info, 20%))}'/%3E%3C/svg%3E%0A");
     --pretix-success-icon: url("data:image/svg+xml,%3Csvg%20viewBox='0%200%2036%2036'%20xmlns='http://www.w3.org/2000/svg'%20xml:space='preserve'%3E%3Crect%20x='5'%20y='5'%20width='26'%20height='26'%20fill='%23fff'/%3E%3Cpath%20d='M25.57%2014.65c0-.23-.1-.46-.26-.62l-1.24-1.24a.89.89%200%200%200-1.24%200l-5.98%206-2.68-2.7a.89.89%200%200%200-1.24%200l-1.24%201.24a.88.88%200%200%200%200%201.24l4.54%204.54a.88.88%200%200%200%201.24%200l7.84-7.84c.17-.16.26-.4.26-.62Z'%20fill='#{url-friendly-colour(darken($in-brand-success, 10%))}'/%3E%3C/svg%3E%0A");
     --pretix-legal-icon: url("data:image/svg+xml,%3Csvg%20viewBox='0%200%2036%2036'%20xmlns='http://www.w3.org/2000/svg'%20xml:space='preserve'%3E%3Ccircle%20cx='18'%20cy='18'%20r='16'%20fill='%23fff'/%3E%3Cpath%20d='M19.41%2011.55c0-.43.2-.79.58-1.08-.42-.27-.99-.4-1.7-.4-.62%200-1.1.13-1.46.4-.36.26-.54.62-.54%201.08%200%20.42.13.76.38%201.01.18.15.5.33.95.57l1.77.85c1.04.48%201.79.9%202.25%201.25.51.36.88.8%201.1%201.3h-.02c.18.38.27.76.27%201.14%200%201.1-.62%202.18-1.85%203.22.48.46.81.9%201%201.3a3.84%203.84%200%200%201-.05%203.07c-.22.5-.54.91-.95%201.26-.42.34-.92.61-1.5.8a6.45%206.45%200%200%201-3.91%200%205.44%205.44%200%200%201-1.6-.79%203.67%203.67%200%200%201-1.1-1.22%203.11%203.11%200%200%201-.36-1.5c0-.66.17-1.2.52-1.59.36-.39.83-.59%201.42-.59.46%200%20.87.16%201.22.48.36.32.53.7.53%201.16%200%20.56-.33%201.03-1%201.41.03.05.07.1.13.13l.2.16a3.24%203.24%200%200%200%201.9.53c.67%200%201.2-.15%201.6-.46.38-.3.58-.7.58-1.22%200-.37-.13-.69-.38-.96a4.46%204.46%200%200%200-1.16-.82l-.9-.44A24.66%2024.66%200%200%201%2015%2020.44a7.7%207.7%200%200%201-.9-.6c-.86-.73-1.29-1.54-1.29-2.45%200-1.16.62-2.23%201.87-3.22a4.7%204.7%200%200%201-.79-1.16%203.38%203.38%200%200%201%20.95-3.98A5.02%205.02%200%200%201%2018.14%208c1.3%200%202.37.3%203.21.91V8.9c.92.6%201.37%201.38%201.37%202.33%200%20.51-.16.93-.49%201.27-.33.34-.75.5-1.26.5a1.6%201.6%200%200%201-1.12-.4c-.3-.28-.44-.62-.44-1.04Zm-1.27%204.66a26.2%2026.2%200%200%201-1.73-.84c-.6.6-.89%201.13-.89%201.6%200%20.34.13.63.39.87.17.15.42.31.74.5a30.57%2030.57%200%200%200%201.93%201l.85.45c.58-.58.87-1.14.87-1.68%200-.36-.15-.67-.46-.94-.3-.27-.87-.6-1.7-.96Z'%20fill='#{url-friendly-colour(darken($in-brand-info, 20%))}'/%3E%3C/svg%3E");
+
+    @if ($in-body-bg = #FFFFFF) {
+      --pretix-body-bg-white-1: 1;
+      --pretix-body-bg-white-0: 0;
+    }
+    @if ($in-body-bg != #FFFFFF) {
+      --pretix-body-bg-white-1: 0;
+      --pretix-body-bg-white-0: 1;
+    }
   }
 }

src/pretix/static/pretixpresale/scss/_theme.scss

@@ -80,39 +80,35 @@ h2.content-header {
 }
 @media (min-width: $screen-sm-min) {
   .main-box {
-    @if ($body-bg != #FFFFFF) {
+    margin: calc(20px * var(--pretix-body-bg-white-0)) auto;
-      margin: 20px auto;
+    padding-left: calc(25px * var(--pretix-body-bg-white-0) + 15px * var(--pretix-body-bg-white-1));
-      padding-left: 25px;
+    padding-right: calc(25px * var(--pretix-body-bg-white-0) + 15px * var(--pretix-body-bg-white-1));
-      padding-right: 25px;
+    border-radius: calc($border-radius-large * var(--pretix-body-bg-white-0));
-      border-radius: $border-radius-large;
-    }
   }
   .page-header-links-outside {
-    @if ($body-bg != #FFFFFF) {
+    padding-left: calc(15px * var(--pretix-body-bg-white-1));
-      padding-left: 0;
+    padding-right: calc(15px * var(--pretix-body-bg-white-1));
-      padding-right: 0;
-    }
   }
   .page-header-links > div.header-part {
-    @if ($body-bg != #FFFFFF) {
+    padding-top: calc(10px * var(--pretix-body-bg-white-0) + 15px * var(--pretix-body-bg-white-1));
-      padding: 10px 0;
+    padding-bottom: calc(10px * var(--pretix-body-bg-white-0));
-      margin-bottom: -20px;
+    padding-left: 0;
+    padding-right: 0;
+    margin-bottom: calc(-20px * var(--pretix-body-bg-white-0));
   }
+  .page-header-links-outside > div.header-part {
+    padding-bottom: calc(15px * var(--pretix-body-bg-white-1));
   }
 
   .page-header.logo-large {
     margin-top: 0;
 
-    @if ($body-bg != #FFFFFF) {
+    margin-left: calc(-25px * var(--pretix-body-bg-white-0));
-      margin-left: -25px;
+    margin-right: calc(-25px * var(--pretix-body-bg-white-0));
-      margin-right: -25px;
-    }
 
     img {
-      @if ($body-bg != #FFFFFF) {
+      border-top-right-radius: calc($border-radius-large * var(--pretix-body-bg-white-0));
-        border-top-right-radius: $border-radius-large;
+      border-top-left-radius: calc($border-radius-large * var(--pretix-body-bg-white-0));
-        border-top-left-radius: $border-radius-large;
-      }
     }
   }
 
@@ -122,9 +118,7 @@ h2.content-header {
 }
 
 footer {
-  @if ($body-bg != #FFFFFF) {
+  padding-bottom: calc(10px * var(--pretix-body-bg-white-1));
-    padding-bottom: 0;
-  }
 }
 
 .label-success-warning {