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/components.css

@@ -0,0 +1,60 @@
+/* Shared components */
+
+/* Content area component */
+section.content-area {
+    h2 {
+        font-size: var(--font-size-lg);
+    }
+
+    .content-area-header {
+        border-bottom: solid 1px var(--secondary-border-color);
+        display: flex;
+        flex-wrap: wrap;
+        column-gap: var(--unit-5);
+        padding-bottom: var(--unit-2);
+        margin-bottom: var(--unit-4);
+
+        h2 {
+            flex: 0 0 auto;
+            line-height: var(--unit-9);
+            margin: 0;
+        }
+
+        .header-controls {
+            flex: 1 1 0;
+            display: flex;
+        }
+    }
+}
+
+@media (max-width: 600px) {
+    section.content-area .content-area-header {
+        flex-direction: column;
+    }
+}
+
+/* Confirm button component */
+span.confirmation {
+    display: flex;
+    align-items: baseline;
+    gap: var(--unit-1);
+    color: var(--error-color) !important;
+
+    svg {
+        align-self: center;
+    }
+
+    .btn.btn-link {
+        color: var(--error-color) !important;
+
+        &:hover {
+            text-decoration: underline;
+        }
+    }
+}
+
+/* Divider */
+.divider {
+    border-bottom: solid 1px var(--secondary-border-color);
+    margin: var(--unit-5) 0;
+}