Fix canvas scroll - use flex display

static/style.css

@@ -75,13 +75,13 @@ input[type="color"] { width: 40px; height: 30px; }
 .toggle-btn.active { background: var(--bg-dark); color: var(--text); border-bottom: 2px solid var(--accent); }
 
 .editor-panel { display: none; flex: 1; overflow: hidden; background: #fff; border-radius: 4px; }
-.editor-panel.active { display: block; }
+.editor-panel.active { display: flex; }
 
 #rich-editor { width: 100%; height: 100%; background: #fff; color: #000; padding: 20px; font-size: 14px; line-height: 1.6; overflow-y: auto; outline: none; }
 
 #drawing-canvas { width: 2000px; height: 2000px; cursor: crosshair; touch-action: none; background: #fff; }
 
-.canvas-scroll-container { width: 100%; height: 100%; overflow: auto; }
+.canvas-scroll-container { width: 100%; height: 100%; overflow: auto; display: flex; }
 
 .status-bar { height: 24px; background: var(--accent); padding: 0 12px; font-size: 11px; display: flex; align-items: center; }