Error CS0246 The type or namespace name 'Form1' could not be found (are you missing a using directive or an assembly code example

Example 1: error CS0246: The type or namespace name 'Slider' could not be found (are you missing a using directive or an assembly reference?)

using UnityEngine.UI;

Example 2: Error CS0246 The type or namespace name 'Form1' could not be found (are you missing a using directive or an assembly

// verif the namespace for Your FORM code must be the same with others
1) form.cs
2) form.design.cs
// refresh and rebuild solution 
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