Custom scss or script

via file:

_includes/assets/custom.js
_includes/assets/custom.scss

via _config.yml:

script: |
  alert("it");
  alert("works!");

scss: |
  .wy-nav-content-wrap{background:#fcfcfc}
  .wy-nav-content-wrap .wy-nav-content{max-width:none}
Tip

Please do not use double slashes in script, and be sure to add the semicolon(;) at the end!