มีหลายแบบ

background-size: contain;

background-size: contain;
background-repeat: no-repeat;

background-size: cover;

background-size: 30%;

background-size: 200px 100px;

https://developer.mozilla.org/en-US/docs/Web/CSS/background-size
https://developer.mozilla.org/en-US/docs/Web/CSS/CSS_Backgrounds_and_Borders/Scaling_background_images