fix: move DevEx Sessions button further left on desktop

[mbagalwa]

Description

This PR adjusts the position of the floating buttons at the bottom-right of the page to fix the overlap between Jump to Top and DevEx Sessions and improve usability.
Problem: The two buttons overlapped or were too close on desktop, making them hard to read and use.
Purpose: Clearly separate the two buttons (Jump to Top on the right, DevEx Sessions to its left) while keeping the same baseline on desktop.

Related Issue Fixes #170

Type of Change

Check the type of change this PR introduces:

• Bug fix (non-breaking change that fixes an issue)
• New feature (non-breaking change that adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update
• Refactor (improves code structure or readability without changing functionality)
• Other (please describe):

Changes Made

website/src/css/custom.css
Desktop (≥768px): Jump to Top button aligned to the right (right: 1.7rem) for consistency with mobile.
Mobile: unchanged (bottom: 4.9rem, right: 1.7rem).
website/src/components/MeetupReminderButton/styles.module.css
Desktop (≥768px): DevEx Sessions button container moved left (right: 2rem → right: 12rem) to avoid overlap with Jump to Top and keep the same baseline.
No business logic changed; only CSS positioning updates.

Checklist

Ensure you have completed the following steps before submitting your PR:

• My code follows the project's coding style and guidelines.
• I have performed a self-review of my own code.
• I have commented my code, particularly in hard-to-understand areas.
• I have updated the documentation (if applicable).
• My changes generate no new warnings or errors.
• I have added tests that prove my fix is effective or that my feature works.
• I have checked for merge conflicts.
• I have rebased my branch onto the latest main or master branch.