What does Skeleton have in its CSS that makes the <sup> tag not work properly?

Question

The <sup> tag does not work well when you are using Skeleton.

So I had to add this code for it to work

sup { font-size: 60%; vertical-align:super; }

I can't find how Skeleton causes this. I have been looking through their 3 CSS files and the only one that deals with fonts is the base.css file

/*
* Skeleton V1.2
* Copyright 2011, Dave Gamache
* www.getskeleton.com
* Free to use under the MIT license.
* http://www.opensource.org/licenses/mit-license.php
* 6/20/2012
*/


/* Table of Content
==================================================
    #Reset & Basics
    #Basic Styles
    #Site Styles
    #Typography
    #Links
    #Lists
    #Images
    #Buttons
    #Forms
    #Misc */


/* #Reset & Basics (Inspired by E. Meyers)
================================================== */
    html, body, div, span, applet, object, iframe, h1, h2, h3, h4, h5, h6, p, blockquote, pre, a, abbr, acronym, address, big, cite, code, del, dfn, em, img, ins, kbd, q, s, samp, small, strike, strong, sub, sup, tt, var, b, u, i, center, dl, dt, dd, ol, ul, li, fieldset, form, label, legend, table, caption, tbody, tfoot, thead, tr, th, td, article, aside, canvas, details, embed, figure, figcaption, footer, header, hgroup, menu, nav, output, ruby, section, summary, time, mark, audio, video {
        margin: 0;
        padding: 0;
        border: 0;
        font-size: 100%;
        font: inherit;
        vertical-align: baseline; }
    article, aside, details, figcaption, figure, footer, header, hgroup, menu, nav, section {
        display: block; }
    body {
        line-height: 1; }
    ol, ul {
        list-style: none; }
    blockquote, q {
        quotes: none; }
    blockquote:before, blockquote:after,
    q:before, q:after {
        content: '';
        content: none; }
    table {
        border-collapse: collapse;
        border-spacing: 0; }


/* #Basic Styles
================================================== */
    body {
        background: #fff;
        font: 14px/21px "HelveticaNeue", "Helvetica Neue", Helvetica, Arial, sans-serif;
        color: #444;
        -webkit-font-smoothing: antialiased; /* Fix for webkit rendering */
        -webkit-text-size-adjust: 100%;
 }


/* #Typography
================================================== */
    h1, h2, h3, h4, h5, h6 {
        color: #181818;
        font-family: "Georgia", "Times New Roman", serif;
        font-weight: normal; }
    h1 a, h2 a, h3 a, h4 a, h5 a, h6 a { font-weight: inherit; }
    h1 { font-size: 46px; line-height: 50px; margin-bottom: 14px;}
    h2 { font-size: 35px; line-height: 40px; margin-bottom: 10px; }
    h3 { font-size: 28px; line-height: 34px; margin-bottom: 8px; }
    h4 { font-size: 21px; line-height: 30px; margin-bottom: 4px; }
    h5 { font-size: 17px; line-height: 24px; }
    h6 { font-size: 14px; line-height: 21px; }
    .subheader { color: #777; }

    p { margin: 0 0 20px 0; }
    p img { margin: 0; }
    p.lead { font-size: 21px; line-height: 27px; color: #777;  }

    em { font-style: italic; }
    strong { font-weight: bold; color: #333; }
    small { font-size: 80%; }

/*  Blockquotes  */
    blockquote, blockquote p { font-size: 17px; line-height: 24px; color: #777; font-style: italic; }
    blockquote { margin: 0 0 20px; padding: 9px 20px 0 19px; border-left: 1px solid #ddd; }
    blockquote cite { display: block; font-size: 12px; color: #555; }
    blockquote cite:before { content: "\2014 \0020"; }
    blockquote cite a, blockquote cite a:visited, blockquote cite a:visited { color: #555; }

    hr { border: solid #ddd; border-width: 1px 0 0; clear: both; margin: 10px 0 30px; height: 0; }


/* #Links
================================================== */
    a, a:visited { color: #333; text-decoration: underline; outline: 0; }
    a:hover, a:focus { color: #000; }
    p a, p a:visited { line-height: inherit; }


/* #Lists
================================================== */
    ul, ol { margin-bottom: 20px; }
    ul { list-style: none outside; }
    ol { list-style: decimal; }
    ol, ul.square, ul.circle, ul.disc { margin-left: 30px; }
    ul.square { list-style: square outside; }
    ul.circle { list-style: circle outside; }
    ul.disc { list-style: disc outside; }
    ul ul, ul ol,
    ol ol, ol ul { margin: 4px 0 5px 30px; font-size: 90%;  }
    ul ul li, ul ol li,
    ol ol li, ol ul li { margin-bottom: 6px; }
    li { line-height: 18px; margin-bottom: 12px; }
    ul.large li { line-height: 21px; }
    li p { line-height: 21px; }

/* #Images
================================================== */

    img.scale-with-grid {
        max-width: 100%;
        height: auto; }


/* #Buttons
================================================== */

    .button,
    button,
    input[type="submit"],
    input[type="reset"],
    input[type="button"] {
        background: #eee; /* Old browsers */
        background: #eee -moz-linear-gradient(top, rgba(255,255,255,.2) 0%, rgba(0,0,0,.2) 100%); /* FF3.6+ */
        background: #eee -webkit-gradient(linear, left top, left bottom, color-stop(0%,rgba(255,255,255,.2)), color-stop(100%,rgba(0,0,0,.2))); /* Chrome,Safari4+ */
        background: #eee -webkit-linear-gradient(top, rgba(255,255,255,.2) 0%,rgba(0,0,0,.2) 100%); /* Chrome10+,Safari5.1+ */
        background: #eee -o-linear-gradient(top, rgba(255,255,255,.2) 0%,rgba(0,0,0,.2) 100%); /* Opera11.10+ */
        background: #eee -ms-linear-gradient(top, rgba(255,255,255,.2) 0%,rgba(0,0,0,.2) 100%); /* IE10+ */
        background: #eee linear-gradient(top, rgba(255,255,255,.2) 0%,rgba(0,0,0,.2) 100%); /* W3C */
      border: 1px solid #aaa;
      border-top: 1px solid #ccc;
      border-left: 1px solid #ccc;
      -moz-border-radius: 3px;
      -webkit-border-radius: 3px;
      border-radius: 3px;
      color: #444;
      display: inline-block;
      font-size: 11px;
      font-weight: bold;
      text-decoration: none;
      text-shadow: 0 1px rgba(255, 255, 255, .75);
      cursor: pointer;
      margin-bottom: 20px;
      line-height: normal;
      padding: 8px 10px;
      font-family: "HelveticaNeue", "Helvetica Neue", Helvetica, Arial, sans-serif; }

    .button:hover,
    button:hover,
    input[type="submit"]:hover,
    input[type="reset"]:hover,
    input[type="button"]:hover {
        color: #222;
        background: #ddd; /* Old browsers */
        background: #ddd -moz-linear-gradient(top, rgba(255,255,255,.3) 0%, rgba(0,0,0,.3) 100%); /* FF3.6+ */
        background: #ddd -webkit-gradient(linear, left top, left bottom, color-stop(0%,rgba(255,255,255,.3)), color-stop(100%,rgba(0,0,0,.3))); /* Chrome,Safari4+ */
        background: #ddd -webkit-linear-gradient(top, rgba(255,255,255,.3) 0%,rgba(0,0,0,.3) 100%); /* Chrome10+,Safari5.1+ */
        background: #ddd -o-linear-gradient(top, rgba(255,255,255,.3) 0%,rgba(0,0,0,.3) 100%); /* Opera11.10+ */
        background: #ddd -ms-linear-gradient(top, rgba(255,255,255,.3) 0%,rgba(0,0,0,.3) 100%); /* IE10+ */
        background: #ddd linear-gradient(top, rgba(255,255,255,.3) 0%,rgba(0,0,0,.3) 100%); /* W3C */
      border: 1px solid #888;
      border-top: 1px solid #aaa;
      border-left: 1px solid #aaa; }

    .button:active,
    button:active,
    input[type="submit"]:active,
    input[type="reset"]:active,
    input[type="button"]:active {
        border: 1px solid #666;
        background: #ccc; /* Old browsers */
        background: #ccc -moz-linear-gradient(top, rgba(255,255,255,.35) 0%, rgba(10,10,10,.4) 100%); /* FF3.6+ */
        background: #ccc -webkit-gradient(linear, left top, left bottom, color-stop(0%,rgba(255,255,255,.35)), color-stop(100%,rgba(10,10,10,.4))); /* Chrome,Safari4+ */
        background: #ccc -webkit-linear-gradient(top, rgba(255,255,255,.35) 0%,rgba(10,10,10,.4) 100%); /* Chrome10+,Safari5.1+ */
        background: #ccc -o-linear-gradient(top, rgba(255,255,255,.35) 0%,rgba(10,10,10,.4) 100%); /* Opera11.10+ */
        background: #ccc -ms-linear-gradient(top, rgba(255,255,255,.35) 0%,rgba(10,10,10,.4) 100%); /* IE10+ */
        background: #ccc linear-gradient(top, rgba(255,255,255,.35) 0%,rgba(10,10,10,.4) 100%); /* W3C */ }

    .button.full-width,
    button.full-width,
    input[type="submit"].full-width,
    input[type="reset"].full-width,
    input[type="button"].full-width {
        width: 100%;
        padding-left: 0 !important;
        padding-right: 0 !important;
        text-align: center; }

    /* Fix for odd Mozilla border & padding issues */
    button::-moz-focus-inner,
    input::-moz-focus-inner {
    border: 0;
    padding: 0;
    }


/* #Forms
================================================== */

    form {
        margin-bottom: 20px; }
    fieldset {
        margin-bottom: 20px; }
    input[type="text"],
    input[type="password"],
    input[type="email"],
    textarea,
    select {
        border: 1px solid #ccc;
        padding: 6px 4px;
        outline: none;
        -moz-border-radius: 2px;
        -webkit-border-radius: 2px;
        border-radius: 2px;
        font: 13px "HelveticaNeue", "Helvetica Neue", Helvetica, Arial, sans-serif;
        color: #777;
        margin: 0;
        width: 210px;
        max-width: 100%;
        display: block;
        margin-bottom: 20px;
        background: #fff; }
    select {
        padding: 0; }
    input[type="text"]:focus,
    input[type="password"]:focus,
    input[type="email"]:focus,
    textarea:focus {
        border: 1px solid #aaa;
        color: #444;
        -moz-box-shadow: 0 0 3px rgba(0,0,0,.2);
        -webkit-box-shadow: 0 0 3px rgba(0,0,0,.2);
        box-shadow:  0 0 3px rgba(0,0,0,.2); }
    textarea {
        min-height: 60px; }
    label,
    legend {
        display: block;
        font-weight: bold;
        font-size: 13px;  }
    select {
        width: 220px; }
    input[type="checkbox"] {
        display: inline; }
    label span,
    legend span {
        font-weight: normal;
        font-size: 13px;
        color: #444; }

/* #Misc
================================================== */
    .remove-bottom { margin-bottom: 0 !important; }
    .half-bottom { margin-bottom: 10px !important; }
    .add-bottom { margin-bottom: 20px !important; }

Additional notes:

• Viewing on Firefox version 27.0.1
• Doctype is <!DOCTYPE html>

Answer 1

First declaration has vertical-align: baseline;