Some initial sass refactoring (breaking change!)

Well, it's not a breaking change if you don't restyle duckquill heavily :)

sass/_code.scss

@@ -0,0 +1,64 @@
+// CODE
+pre,
+code,
+kbd {
+    font-family: var(--font-monospace-code);
+}
+
+code:not(pre code) {
+    box-shadow: var(--edge-highlight);
+    border-radius: var(--rounded-corner-small);
+    background-color: var(--fg-muted-2);
+    padding: 0.125rem 0.375rem;
+    color: var(--red-fg);
+}
+
+pre {
+    margin: 1rem 0 1rem;
+    box-shadow: var(--edge-highlight), var(--shadow);
+    border-radius: var(--rounded-corner);
+    padding: 1rem;
+    max-width: 100vw;
+    overflow: auto;
+    line-height: normal;
+
+    table td {
+        border: none;
+        padding: 0;
+    }
+
+    // The line number cells
+    table td:nth-of-type(1) {
+        user-select: none;
+        text-align: center;
+    }
+
+    mark {
+        display: block;
+        box-shadow: none;
+        border-radius: 0; // Unset code block border radius
+        background-color: var(--fg-muted-1);
+        padding: 0; // Unset mark padding
+        color: var(--fg-color); // Unset mark color from primary color to text color
+    }
+
+    table {
+        box-shadow: none;
+        border-radius: 0;
+        border-collapse: collapse;
+        width: 100%;
+        table-layout: auto;
+        overflow: auto;
+
+        tr {
+            &:nth-child(even) {
+                background-color: unset;
+            }
+        }
+    }
+
+    // The line numbers already provide some kind of left/right padding
+    &[data-linenos] {
+        padding: 1rem 0;
+    }
+}