Update mobile.css

[FNICKE]

Description

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Checklist

• I've been assigned an issue related to this PR.
• I've used beautifiers.
• I've added my Project's name and description to Index.md
• I've made a README.md file for my Project.
• The README.md file of my projrct contains Project title, Description, Use of project, Set up, Stack used and Output (Screenshots).

Related Issues or Pull Requests number

Summary

This PR enhances the overall user interface and experience of the ArtGallery web project.

Changes Made

• Redesigned header to be responsive and visually consistent
• Refactored gallery image layout for better mobile display using Flexbox and Grid
• Improved About and Contact sections with modern font sizes, spacing, and readability
• Styled the contact form with proper labels, input spacing, and hover interactions
• Updated mobile.css for better performance across breakpoints

Screenshots

(Add before/after screenshots if possible)

Checklist

• Mobile-friendly layout
• Image responsiveness and hover effect
• Accessible and clean form fields
• Footer and color scheme improvements