Reorganize CSS files (#24739)

Reorganize various CSS files for clarity, group together by subdirectory
in `index.css`. This reorders some of the rules, but I don't think it
should introduce any issues because of that.

web_src/css/features/tribute.css

@@ -0,0 +1,42 @@
+@import "tributejs/dist/tribute.css";
+
+.tribute-container {
+  box-shadow: 0 0.25rem 0.5rem rgba(0, 0, 0, 0.25);
+  border-radius: 0.25rem;
+}
+
+.tribute-container ul {
+  margin-top: 0 !important;
+  background: var(--color-body) !important;
+}
+
+.tribute-container li {
+  padding: 3px 0.5rem !important;
+}
+
+.tribute-container li span.fullname {
+  font-weight: normal;
+  font-size: 0.8rem;
+  margin-left: 3px;
+}
+
+.tribute-container li.highlight,
+.tribute-container li:hover {
+  background: var(--color-primary) !important;
+  color: var(--color-primary-contrast) !important;
+}
+
+.tribute-item {
+  display: flex;
+  align-items: center;
+}
+
+.tribute-item .emoji,
+.tribute-item img[src*="/avatar/"] {
+  margin-right: 0.5rem;
+}
+
+.tribute-container img {
+  width: 1.5rem !important;
+  height: 1.5rem !important;
+}