Place CSS into React Components

We have a project with 17-25 fairly simple React components (including pages. We've got a graphic designer who says they'll give us CSS for some mockups. So we need you to enter the CSS into the components. The pages and components include: (1) a minmal header including a logo and 2 buttons (2) basic login (two fields) and onboarding (six fields) forms (3) a simple landing page [consisting of the header, 3 buttons, and 3 pictures that change upon hovering] (4) a data entry form, consisting of a display of current info (probably two columns) and buttons for record creation and deletion. Current data can be updated as well. (5) a data display field, including 2 pull-downs to select data to view and the output of the data selected. These elements are working in React, and the mockups are basically created. The designer is planning on creating CSS3 grids/flexbox.