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/code.css

@@ -0,0 +1,30 @@
+/* Code */
+:root {
+    --code-bg-color: var(--body-color-contrast);
+    --code-color: var(--text-color);
+}
+
+code {
+    border-radius: var(--border-radius);
+    line-height: 1.25;
+    padding: .1rem .2rem;
+    background: var(--code-bg-color);
+    color: var(--code-color);
+    font-size: 85%;
+}
+
+.code {
+    border-radius: var(--border-radius);
+    background: var(--code-bg-color);
+    color: var(--text-color);
+    position: relative;
+
+    & code {
+        color: inherit;
+        display: block;
+        line-height: 1.5;
+        overflow-x: auto;
+        padding: var(--unit-2);
+        width: 100%;
+    }
+}