Theme improvements (#822)

* start converting

* small fixes

* reorganize theme files

* cleanup search bar

* increase spacing

* small tweaks

* fix select styles in Chrome

* cleanup menus

* improve button icons

* restore badges

* remove unused classes

* restore some overrides

* restore bookmark form

* add summary outline

* avoid layout shifts

* restore bookmark details

* increase border radius for modals

* improve details modal

* restore reader mode

* restore settings

* cleanup variables

* start with dark theme

* more dark theme...

* more light theme...

* more dark theme...

* add postcss build

* remove sass processor

* update docker build

* fix alt color

* remove endless symbol

* fix tests

* update assets

* remove sass files

* fix docker build

* cleanup spacing

* improve theme

* update test scripts

* update CI workflow

* fix test

bookmarks/styles/markdown.css

@@ -0,0 +1,40 @@
+.markdown {
+    & p, & ul, & ol, & pre, & blockquote {
+        margin: 0 0 var(--unit-2) 0;
+    }
+
+    & > *:first-child {
+        margin-top: 0;
+    }
+
+    & > *:last-child {
+        margin-bottom: 0;
+    }
+
+    & ul, & ol {
+        margin-left: var(--unit-4);
+    }
+
+    & ul li, & ol li {
+        margin-top: var(--unit-1);
+    }
+
+    & pre {
+        padding: var(--unit-1) var(--unit-2);
+        background-color: var(--code-bg-color);
+        border-radius: var(--unit-1);
+        overflow-x: auto;
+    }
+
+    & pre code {
+        background: none;
+        box-shadow: none;
+        padding: 0;
+    }
+
+    & > pre:first-child:last-child {
+        padding: 0;
+        background: none;
+        border-radius: 0;
+    }
+}