In VSCode, these green curved lines indicate a warning in the code. VSCode performs background code analysis ( Linting ) to provide you feedback on syntax and compilation errors.
In your particular case, this is because the CSS ruleset is empty (declaration of selector, but no properties). You can see the warning message by hovering over the code with a green line below it.
You can disable the waveline by disabling listing for CSS.
→ → , .json
"css.validate": false
, "css.lint.emptyRules": ""
HTML JavaScript.