amp-module adds a custom class to body tag of page, you may use __amp class to target elements only in AMP pages.
.__amp .my-awesome-element {
}However we recommend to create a separate style file for AMP pages and import it in AMP layout, also remove styles from nuxt.config and import those files in default layout instead.
// default.vue
...
<style>
@import "~/assets/styles/default.css"
</style>And AMP layout
// default.amp.vue
...
<style>
@import "~/assets/styles/default.amp.css"
</style>