refactor(frontend): prefix css variables (UI) (#14739)

* refactor(frontend): prefix css variables

* `MI_UI` -> `MI`

* fix

* `stickyBottom`

* stickyTop

packages/frontend/src/components/global/MkPageHeader.vue

@@ -130,8 +130,8 @@ onUnmounted(() => {
 
 <style lang="scss" module>
 .root {
-	-webkit-backdrop-filter: var(--blur, blur(15px));
-	backdrop-filter: var(--blur, blur(15px));
+	-webkit-backdrop-filter: var(--MI-blur, blur(15px));
+	backdrop-filter: var(--MI-blur, blur(15px));
 	border-bottom: solid 0.5px var(--MI_THEME-divider);
 	width: 100%;
 }
@@ -145,7 +145,7 @@ onUnmounted(() => {
 .upper {
 	--height: 50px;
 	display: flex;
-	gap: var(--margin);
+	gap: var(--MI-margin);
 	height: var(--height);
 
 	.tabs:first-child {