[Feature] consistently use single quotes in CSS files

## Problem
Inconsistent use of quotation styles in normalize.css file (single vs. double quotes) can reduce code readability, introduce unnecessary diffs in version control, and complicate style enforcement across teams. This inconsistency also makes it harder to apply automated linting rules.
with reference to #322

## Description
Standardizing the use of single quotes in the normalize.css file ensures consistency across the codebase. This improvement enhances readability, simplifies collaboration, and allows for seamless integration with automated linting tools.

## Alternatives
1. Stick with double quotes: While valid, this approach may not align with established preferences and would require similar enforcement.
2. Allow both styles: This would avoid standardization but negates the benefits of readability, linting, and reduced version control diffs.

## Additional context
Using single quotes aligns normalize.css with broader project conventions if single quotes are preferred across the CSS codebase. It also integrates well with stylelint rules, such as string-quotes: 'single', to enforce consistency.

## Implementation

- [X] I would be interested in implementing this feature.

Start by locating normalize.css and comparing its quotation marks with the conventions used in the other CSS files. Standardize the file on single quotes, then run the project's CSS linting if available and confirm no inconsistent double-quoted strings remain.

Written by the indexing model from the issue text.