feat: enhance modal positioning and animation for improved user exper…

[Degalax]

This pull request updates the modal styling in the Planning page to improve its positioning and appearance. The main changes focus on centering the modal, refining its animation, and adjusting the overlay styles for better user experience.

Modal positioning and appearance improvements:

• Centered the .planning-modal both vertically and horizontally using position: fixed, top: 50%, left: 50%, and transform: translate(-50%, -50%). Also updated the animation keyframes to match the new centering logic.
• Adjusted the modal's width to calc(100% - 2rem) for better responsiveness and set a higher z-index to ensure it appears above the overlay.

Overlay style adjustments:

• Removed flexbox centering and padding from the overlay, and added border: none and cursor: default for a cleaner, less interactive background.…ience