Enhance SkillTreeMultiSelect Component and CSS Styles

- Updated the SkillTreeMultiSelect component to support dynamic positioning and improved accessibility through the use of portals.
- Refactored the dropdown panel rendering logic to enhance user experience when selecting skills.
- Added CSS styles for the exercise filter modal to improve layout and responsiveness.
- Introduced new styles for the skill tree multiselect panel, ensuring better visual integration and usability.

frontend/src/app.css

@@ -4086,6 +4086,12 @@ html.modal-scroll-locked .app-main {
 
 .exercise-filter-modal.admin-modal-sheet {
   max-width: min(920px, calc(100dvw - 16px));
+  max-height: min(92vh, 920px);
+}
+@media (min-width: 640px) {
+  .exercise-filter-modal.admin-modal-sheet {
+    max-height: min(90vh, 920px);
+  }
 }
 .exercise-filter-modal .admin-modal-sheet__body.exercise-filter-modal__scroll {
   flex: 1;
@@ -6418,6 +6424,24 @@ html.modal-scroll-locked .app-main {
   max-height: min(360px, 55vh);
   overflow: auto;
 }
+.skill-tree-multiselect__panel--portal {
+  position: fixed;
+  right: auto;
+  top: auto;
+  overflow: auto;
+  -webkit-overflow-scrolling: touch;
+}
+.skill-tree-multiselect__panel--portal .multiselect-combo__list {
+  position: static;
+  left: auto;
+  right: auto;
+  top: auto;
+  margin: 0;
+  max-height: none;
+  box-shadow: none;
+  border: none;
+  border-radius: 0;
+}
 .skill-tree {
   list-style: none;
   margin: 0;

frontend/src/components/SkillTreeMultiSelect.jsx

@@ -1,7 +1,12 @@
-import React, { useCallback, useEffect, useMemo, useRef, useState } from 'react'
+import React, { useCallback, useEffect, useLayoutEffect, useMemo, useRef, useState } from 'react'
+import { createPortal } from 'react-dom'
 import { collectSkillLeavesFromTree, buildSkillCatalogTree } from '../utils/skillCatalogTree'
 import SkillTreePickerPanel from './SkillTreePickerPanel'
 
+const PANEL_MAX_HEIGHT = 360
+const PANEL_MIN_HEIGHT = 140
+const PANEL_Z_INDEX = 1100
+
 function normId(id) {
   return String(id)
 }
@@ -17,11 +22,15 @@ export default function SkillTreeMultiSelect({
   browseLabel = '▼ Katalog',
   emptyHint = 'Keine Treffer',
   className = '',
+  usePortal = true,
 }) {
   const [query, setQuery] = useState('')
   const [open, setOpen] = useState(false)
   const [browseTree, setBrowseTree] = useState(false)
+  const [panelStyle, setPanelStyle] = useState(null)
   const rootRef = useRef(null)
+  const fieldRef = useRef(null)
+  const panelRef = useRef(null)
 
   const tree = useMemo(() => buildSkillCatalogTree(skills), [skills])
   const selectedSet = useMemo(() => new Set(value.map(normId)), [value])
@@ -56,17 +65,99 @@ export default function SkillTreeMultiSelect({
 
   useEffect(() => {
     const onDoc = (e) => {
-      if (!rootRef.current?.contains(e.target)) {
-        setOpen(false)
-        setBrowseTree(false)
-      }
+      const t = e.target
+      if (rootRef.current?.contains(t) || panelRef.current?.contains(t)) return
+      setOpen(false)
+      setBrowseTree(false)
     }
     document.addEventListener('mousedown', onDoc)
     return () => document.removeEventListener('mousedown', onDoc)
   }, [])
 
+  const updatePanelPosition = useCallback(() => {
+    const anchor = fieldRef.current
+    if (!anchor) return
+    const rect = anchor.getBoundingClientRect()
+    const gap = 4
+    const margin = 12
+    const spaceBelow = window.innerHeight - rect.bottom - gap - margin
+    const spaceAbove = rect.top - gap - margin
+    const openUp = spaceBelow < PANEL_MIN_HEIGHT && spaceAbove > spaceBelow
+    const available = Math.max(0, openUp ? spaceAbove : spaceBelow)
+    const maxHeight = Math.min(PANEL_MAX_HEIGHT, Math.max(PANEL_MIN_HEIGHT, available))
+    const top = openUp ? Math.max(margin, rect.top - gap - maxHeight) : rect.bottom + gap
+
+    setPanelStyle({
+      position: 'fixed',
+      left: rect.left,
+      width: rect.width,
+      top,
+      maxHeight,
+      zIndex: PANEL_Z_INDEX,
+    })
+  }, [])
+
+  useLayoutEffect(() => {
+    if (!open || !usePortal) {
+      setPanelStyle(null)
+      return undefined
+    }
+    updatePanelPosition()
+    window.addEventListener('resize', updatePanelPosition)
+    window.addEventListener('scroll', updatePanelPosition, true)
+    return () => {
+      window.removeEventListener('resize', updatePanelPosition)
+      window.removeEventListener('scroll', updatePanelPosition, true)
+    }
+  }, [open, usePortal, updatePanelPosition, query, browseTree, value.length])
+
   const showTree = browseTree || !query.trim()
 
+  const panelContent = showTree ? (
+    <SkillTreePickerPanel
+      skills={skills}
+      excludeIds={value}
+      searchQuery={query}
+      onPickSkill={(id) => addId(id)}
+      pickMode="multi"
+    />
+  ) : (
+    <ul className="multiselect-combo__list" role="listbox">
+      {leaves.filter((l) => l.pathLabel.toLowerCase().includes(query.trim().toLowerCase())).length === 0 ? (
+        <li className="multiselect-combo__empty">{emptyHint}</li>
+      ) : (
+        leaves
+          .filter((l) => l.pathLabel.toLowerCase().includes(query.trim().toLowerCase()))
+          .map((l) => (
+            <li key={normId(l.id)}>
+              <button
+                type="button"
+                className="multiselect-combo__opt skill-tree__pick--path"
+                onMouseDown={(e) => e.preventDefault()}
+                onClick={() => addId(l.id)}
+              >
+                <span className="skill-tree__pick-name">{l.label}</span>
+                <span className="skill-tree__pick-path">{l.pathLabel}</span>
+              </button>
+            </li>
+          ))
+      )}
+    </ul>
+  )
+
+  const dropdownPanel =
+    open && (usePortal ? panelStyle : true) ? (
+      <div
+        ref={panelRef}
+        className={
+          'skill-tree-multiselect__panel' + (usePortal ? ' skill-tree-multiselect__panel--portal' : '')
+        }
+        style={usePortal ? panelStyle : undefined}
+      >
+        {panelContent}
+      </div>
+    ) : null
+
   return (
     <div className={`multiselect-combo skill-tree-multiselect ${className}`.trim()} ref={rootRef}>
       <div className="multiselect-combo__chips">
@@ -85,7 +176,7 @@ export default function SkillTreeMultiSelect({
           </button>
         ))}
       </div>
-      <div className="multiselect-combo__field">
+      <div className="multiselect-combo__field" ref={fieldRef}>
         <input
           type="text"
           className="form-input multiselect-combo__input"
@@ -113,42 +204,8 @@ export default function SkillTreeMultiSelect({
           {browseLabel}
         </button>
       </div>
-      {open ? (
-        <div className="skill-tree-multiselect__panel">
-          {showTree ? (
-            <SkillTreePickerPanel
-              skills={skills}
-              excludeIds={value}
-              searchQuery={query}
-              onPickSkill={(id) => addId(id)}
-              pickMode="multi"
-            />
-          ) : (
-            <ul className="multiselect-combo__list" role="listbox">
-              {leaves.filter((l) => l.pathLabel.toLowerCase().includes(query.trim().toLowerCase())).length ===
-              0 ? (
-                <li className="multiselect-combo__empty">{emptyHint}</li>
-              ) : (
-                leaves
-                  .filter((l) => l.pathLabel.toLowerCase().includes(query.trim().toLowerCase()))
-                  .map((l) => (
-                    <li key={normId(l.id)}>
-                      <button
-                        type="button"
-                        className="multiselect-combo__opt skill-tree__pick--path"
-                        onMouseDown={(e) => e.preventDefault()}
-                        onClick={() => addId(l.id)}
-                      >
-                        <span className="skill-tree__pick-name">{l.label}</span>
-                        <span className="skill-tree__pick-path">{l.pathLabel}</span>
-                      </button>
-                    </li>
-                  ))
-              )}
-            </ul>
-          )}
-        </div>
-      ) : null}
+      {!usePortal && dropdownPanel}
+      {usePortal && dropdownPanel ? createPortal(dropdownPanel, document.body) : null}
     </div>
   )
 }