fix code background color

Thanks for creating this useful project! Here's a small fix:

Code in proto comments like this:

syntax = "proto3";

package sable.test.v1;

// Example 1: Compute Timestamp from POSIX `time()`.
//
//     Timestamp timestamp;
//     timestamp.set_seconds(time(NULL));
//     timestamp.set_nanos(0);
//
message SmallMessage {
    string foo = 1;
}

Which you find in places like this.

Render like this in dark mode:

code-in-darkmode-current

This change makes them render like this instead:

code-in-darkmode-fixed

markvincze / sabledocs

fix code background color #35