BoundsExtensions.cs

using UnityEngine;

public static class BoundsExtensions
{
    /// <summary>
    /// Modifies the bounds center position so that it's min and max are within the container
    /// It doesnt modify the bounds size, if bounds are larger then the container it will be centered
    /// </summary>
    public static void MoveInside(ref this Bounds bounds, Bounds container)
    {
        bounds.center = ClampWithSize(bounds.center, bounds.size, container.min, container.max);
    }

    private static Vector3 ClampWithSize(Vector3 center, Vector3 size, Vector3 min, Vector3 max)
    {
        for (int i = 0; i < 3; i++) { center[i] = ClampWithSize(center[i], size[i], min[i], max[i]); }
        return center;
    }

    private static float ClampWithSize(float center, float size, float min, float max)
    {
        float containerSize = max - min;
        //if the size cant be contained in the other put it in the middle
        if (size > containerSize) { return containerSize * 0.5f + min; }

        float extent = size * 0.5f;
        return Mathf.Clamp(center, min + extent, max - extent);
    }
}