hiya! not a bother. you can change them (they are currently set to custom icons actually). the pixel size i used is 16x16 and they all fit without any issue. 

these are what i used. sorry they are not labeled... put these under the import link. 

.side-nav {
  .sidebar-tab i::before {
    content: url(image_url) !important;
  }
 
  .sidebar-li-gallery i::before {
    content: url(image_url) !important;
  }
 
  .sidebar-li-library i::before {
    content: url(image_url) !important;
  }
 
  .sidebar-li-worlds i::before {
    content: url(image_url) !important;
  }
 
  .sidebar-li-links i::before {
    content: url(image_url) !important;
  }
 
  .character-folder i::before {
    content: url(image_url) !important;
  }
 
  .sidebar-li-comments i::before {
    content: url(image_url) !important;
  }
 
  .sidebar-li-favorites i::before {
    content: url(image_url) !important;
  }
 
  .sidebar-li-ownership i::before {
    content: url(image_url) !important;
  }
 
  .sidebar-li-report i::before {
    content: url(image_url) !important;
  }
 
  .sidebar-li-block i::before {
    content: url(image_url) !important;
  }
 
  .character-manage-subheader i:before {
    content: url(image_url) !important;
  }
 
  .sidebar-li-literatures i::before {
    content: url(image_url) !important;
  }
 
  .sidebar-li-characters i::before {
    content: url(image_url) !important;
  }
 
  .sidebar-li-bulletins i::before {
    content: url(image_url) !important;
  }
 
  .sidebar-li-stats i::before {
    content: url(image_url) !important;
  }
 
  .sidebar-li-art i::before {
    content: url(image_url) !important;
  }
 
  .sidebar-li-created i::before {
    content: url(image_url) !important;
  }
 
  .sidebar-li-message i::before {
    content: url(image_url) !important;
  }
 
  .sidebar-li-unsubscribe i::before, .sidebar-li-subscribe i::before {
    content: url(image_url) !important;
  }
 
  .sidebar-li-unauthorize i::before, .sidebar-li-authorize i::before {
    content: url(image_url) !important;
  }
}