Useful

• https://css-tricks.com/
• https://caniuse.com/
• https://web.dev/
• https://tools.pingdom.com/

Notes with various snippets

• HTML (Image for upload button) input[type=file] https://blog.benestudio.co/custom-file-upload-button-with-pure-css-5aacf39aa0a
• Custom styles (for e.g. button wp) https://codex.wordpress.org/TinyMCE_Custom_Styles