fix(submit): raise TinyMCE fullscreen above the fixed navbar

TinyMCE's skin injects .mce-fullscreen { z-index: 100 } at editor init,
after core editor.css, so the fullscreen editor (toolbar at the viewport
top) lost to the fixed navbar (.nav-fixed .header, z-index 999). Restore
core's intended 100010 with an element+class selector that outranks the
skin regardless of injection order; it stays below the submit media
dialog (100080). Also remove the dead .mce-top-part.affix rules (no
AKSRT script drives them) and pin both in a contract test.

assets/css/frontend/pages/submit.css

@@ -51,19 +51,18 @@
   border: 0;
 }
 
-.newposts-editor .mce-top-part.affix {
-  position: fixed;
-}
-
-.newposts-editor .mce-top-part.affix-bottom {
-  position: absolute;
-}
-
 .newposts-editor .wp-editor-container {
   overflow: hidden;
   border-radius: 0;
 }
 
+/* TinyMCE 全屏容器：skin 样式在编辑器初始化时注入（晚于核心 editor.css），
+   其 .mce-fullscreen 的 z-index:100 压不过固定导航栏（.nav-fixed .header 为 999）。
+   用元素+类选择器提高优先级，恢复 WP 核心预期的 100010，仍低于投稿媒体弹层（100080）。 */
+div.mce-fullscreen {
+  z-index: 100010;
+}
+
 .newposts-editor .mce-toolbar-grp,
 .newposts-editor div.mce-toolbar-grp {
   border-bottom: 0;
@@ -547,12 +546,30 @@ body.aksrt-editor-media-open {
   font-size: 1em;
 }
 
+/* 纯图标按钮（设置视频封面/视频/清除）：fa 字形行高与文字不同导致图标上偏，
+   用 flex 居中修正；并去掉 legacy .but 给图标加的文字间距。btn-delete 的
+   hidden 属性切换依赖默认 display，故用 :not([hidden]) 守卫。 */
+.featured-edit .btns-full .btn-video,
+.featured-edit .btns-full .btn-delete:not([hidden]) {
+  display: inline-flex;
+  align-items: center;
+  justify-content: center;
+}
+
 .featured-edit .btns-full .btn-video-pic {
   display: none;
 }
 
 .featured-loaded.video .btns-full .btn-video-pic {
   display: inline-flex;
+  align-items: center;
+  justify-content: center;
+}
+
+.featured-edit .btns-full .btn-video-pic > .fa,
+.featured-edit .btns-full .btn-video > .fa,
+.featured-edit .btns-full .btn-delete > .fa {
+  margin-right: 0;
 }
 
 .featured-loaded.image .btn-video,