Under Settings > Customization > Job Ads, you have the option to add a header image and logo to your job ads, upload a preview image for your social channels, and adjust the colors.
Recommended resolutions for optimal display:
Logo: 360 x 90px
Header image: 940 x 225px
Preview image: 1111 x 583px
Starting with the Pro plan, a variety of advanced customization options for your jobs are available to you.