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/theme/dropdowns.css

@@ -0,0 +1,36 @@
+/* Dropdown */
+.dropdown {
+  display: inline-block;
+  position: relative;
+
+  .menu {
+    animation: fade-in .15s ease 1;
+    display: none;
+    left: 0;
+    max-height: 50vh;
+    overflow-y: auto;
+    position: absolute;
+    top: 100%;
+  }
+
+  &.dropdown-right {
+    .menu {
+      left: auto;
+      right: 0;
+    }
+  }
+
+  &.active .menu,
+  .dropdown-toggle:focus + .menu,
+  .menu:hover {
+    display: block;
+  }
+
+  /* Fix dropdown-toggle border radius in button groups */
+  .btn-group {
+    .dropdown-toggle:nth-last-child(2) {
+      border-bottom-right-radius: var(--border-radius);
+      border-top-right-radius: var(--border-radius);
+    }
+  }
+}