Shiki theme not applying on code block background

[Neluji]

Describe the bug

When using a theme for shiki, the colours are effectively applied to the text, but the background of the code blocks remains in the default colour.

Minimal reproduction

Steps to reproduce the behavior:

1. Create a new Slidev project:

   npm init slidev@latest / pnpm create slidev / yarn create slidev

   and install the dependencies
2. In the project, create a setup folder, and in it, a shiki.ts file (as specified in the doc) with the following content:

   /* ./setup/shiki.ts */
   import { defineShikiSetup } from "@slidev/types";
   
   export default defineShikiSetup(() => {
     return {
       themes: {
         dark: "min-light",
         light: "min-dark",
       },
     };
   });

   this should apply a dark theme to the code when in light mode, and vice-versa
3. Launch the dev server and open the slide using the dev npm script
4. Go to the 5th slide where there is some code blocks: the colour of the code is the one from the shiki theme (i.e. colours of the min-dark code theme when in light mode and vice-versa), but the background remains the default one (i.e. a light background when in light mode and vice-versa)

System infos

• Slidev version: 51.0.2
• Browser: Firefox
• OS: Ubuntu