vaadin 14 grid

Grid header color change any idea?:weary:

[part=“cell header-cell”] {
background-color: #1da834;
}

in /frontend/themes//components/vaadin-grid.css

ok sir

addThemeVariants(GridVariant.LUMO_COLUMN_BORDERS); I want to thick the line ?

Instead of asking I recommend to learn about component styling:
https://vaadin.com/docs/latest/components/ds-resources/customization/styling-components