Upgrade SPFx Applications Customizer CSS Injection extension to latest version of SPFx - Refresh Rangers Hacktoberfest Event

[Adam-it]

🎯Aim

The aim of this issue is to upgrade the SPFx Applications Customizer CSS Injection extension sample to the latest version of SPFx (1.20)

🤔 Tips how to get started

To support you in this issue you may use the below tooling:

• CLI for Microsoft 365 has a command that will generate upgrade guidance for this SPFx project m365 spfx project upgrade
• SPFx Toolkit VS Code extension has an Upgrade Project action which generates an .md report with upgrade guidance to the latest supported SPFx version

📣 What's this event all about

Refresh Rangers is a unique Hacktoberfest event aiming to update our most popular samples 🚀.
During this, you may obtain a unique Microsoft 365 & Power Platform Community badge - Refresh Rangers 🎖️
To obtain this badge besides opening a PR you also need to opt-in the Microsoft 365 & Power Platform Community Recognition Program and fill out this form

[tom-daly]

PR submitted for this one

[Adam-it]

PR submitted for this one

That is just so awesome 👏👏👏
You Rock 🤩
In future please try to go the other way around. first let us know in issue that you are interested and open a PR only after you get assigned. 🙏 It's a good practice to keep in order to avoid conflicts and multiple people working on the same stuff.

Also to get a badge from Microsoft 365 & Power Platform community you need to join the recognition program: https://pnp.github.io/recognitionprogram/
You only need to do that one time so if you done already in the past you don't need to fill the form again.

To get a badge from the Hacktoberfest organizers you need to register to Hacktoberfest event: https://hacktoberfest.com/participation/