Ghost/ghost/staff-service/lib/email-templates/partials/styles.hbs

<style>
  /* -------------------------------------
      RESPONSIVE AND MOBILE FRIENDLY STYLES
  ------------------------------------- */
  @media only screen and (max-width: 620px) {
    table[class=body] h1 {
      font-size: 28px !important;
      margin-bottom: 10px !important;
    }
    table[class=body] p,
    table[class=body] ul,
    table[class=body] ol,
    table[class=body] td,
    table[class=body] span,
    table[class=body] a {
      font-size: 16px !important;
    }
    table[class=body] .wrapper,
    table[class=body] .article {
      padding: 10px !important;
    }
    table[class=body] .content {
      padding: 0 !important;
    }
    table[class=body] .container {
      padding: 0 !important;
      width: 100% !important;
    }
    table[class=body] .main {
      border-left-width: 0 !important;
      border-radius: 0 !important;
      border-right-width: 0 !important;
    }
    table[class=body] .btn table {
      width: 100% !important;
    }
    table[class=body] .btn a {
      width: 100% !important;
    }
    table[class=body] .img-responsive {
      height: auto !important;
      max-width: 100% !important;
      width: auto !important;
    }
    table[class=body] p[class=small],
    table[class=body] a[class=small] {
      font-size: 11px !important;
    }
    .new-mention-thumbnail {
      display: none !important;
    }
  }
  /* -------------------------------------
      PRESERVE THESE STYLES IN THE HEAD
  ------------------------------------- */
  @media all {
    .ExternalClass {
      width: 100%;
    }
    .ExternalClass,
    .ExternalClass p,
    .ExternalClass span,
    .ExternalClass font,
    .ExternalClass td,
    .ExternalClass div {
      line-height: 100%;
    }
    /* Reset styles for Gmail (it wraps email address in link with custom styles) */
    .text-link a {
      color: inherit !important;
      font-family: inherit !important;
      font-size: inherit !important;
      font-weight: inherit !important;
      line-height: inherit !important;
      text-decoration: none !important;
    }
    #MessageViewBody a {
      color: inherit;
      text-decoration: none;
      font-size: inherit;
      font-family: inherit;
      font-weight: inherit;
      line-height: inherit;
    }
  }
  hr {
    border-width: 0;
    height: 0;
    margin-top: 34px;
    margin-bottom: 34px;
    border-bottom-width: 1px;
    border-bottom-color: #EEF5F8;
  }
  a {
    color: #15212A;
  }
  blockquote {
    margin-left: 0;
    padding-left: 20px;
    border-left: 3px solid #DDE1E5;
  }
</style>