Frontend iframe renderer framework: 3D models, OpenAPI (#37233) (#37273)

Backport

* #37233
* #37272

---------

Co-authored-by: silverwind <me@silverwind.io>

web_src/css/markup/content.css

@@ -458,9 +458,11 @@ html[data-gitea-theme-dark="false"] .markup img[src*="#gh-dark-mode-only"] {
 }
 
 .external-render-iframe {
+  display: block; /* removes the inline baseline gap below the iframe */
   width: 100%;
   height: max(300px, 80vh);
   border: none;
+  border-radius: 0 0 var(--border-radius) var(--border-radius);
 }
 
 .markup-content-iframe {

web_src/css/swagger-render.css

@@ -1,9 +1,5 @@
 @import "../../node_modules/swagger-ui-dist/swagger-ui.css";
 
-body {
-  margin: 0;
-}
-
 html,
 html body,
 html .swagger-ui,
@@ -15,27 +11,3 @@ html .swagger-ui .scheme-container {
 html.dark-mode .swagger-ui table.headers td {
   color: var(--color-text) !important;
 }
-
-.swagger-back-link {
-  color: var(--color-primary);
-  text-decoration: none;
-  position: absolute;
-  top: 1rem;
-  right: 1.5rem;
-  display: flex;
-  align-items: center;
-}
-
-.swagger-back-link:hover {
-  text-decoration: underline;
-}
-
-.swagger-back-link svg {
-  color: inherit;
-  fill: currentcolor;
-  margin-right: 0.5rem;
-}
-
-.swagger-spec-content {
-  display: none;
-}

web_src/css/swagger-standalone.css

@@ -0,0 +1,29 @@
+@import "swagger-render.css";
+
+body {
+  margin: 0;
+}
+
+.swagger-back-link {
+  color: var(--color-primary);
+  text-decoration: none;
+  position: absolute;
+  top: 1rem;
+  right: 1.5rem;
+  display: flex;
+  align-items: center;
+}
+
+.swagger-back-link:hover {
+  text-decoration: underline;
+}
+
+.swagger-back-link svg {
+  color: inherit;
+  fill: currentcolor;
+  margin-right: 0.5rem;
+}
+
+.swagger-spec-content {
+  display: none;
+}