diagnostic.css

/* content styles */
applet:hover:after, basefont:hover:after, center:hover:after, dir:hover:after, font:hover:after, isindex:hover:after, menu:hover:after, strike:hover:after, s:hover:after, u:hover:after, *[background]:hover:after, *[bgcolor]:hover:after, *[clear]:hover:after, *[color]:hover:after, *[compact]:hover:after, *[noshade]:hover:after, *[nowrap]:hover:after, *[size]:hover:after, *[start]:hover:after, *[bottommargin]:hover:after, *[leftmargin]:hover:after, *[rightmargin]:hover:after, *[topmargin]:hover:after, *[marginheight]:hover:after, *[marginwidth]:hover:after, *[alink]:hover:after, *[link]:hover:after, *[text]:hover:after, *[vlink]:hover:after, *[align]:hover:after, *[valign]:hover:after, *[hspace]:hover:after, *[vspace]:hover:after, *[height]:hover:after, *[width]:hover:after, ul[type]:hover:after, ol[type]:hover:after, li[type]:hover:after, iframe:not([title]):hover:after, div[role="img"]:not([aria-label]):hover:after, a[href=""]:hover:after, a[href="#"]:hover:after, a:not([href]):hover:after, a[href*=javascript\:]:hover:after, a[onclick]:hover:after, a[href=""]:focus:after, a[href="#"]:focus:after, a:not([href]):focus:after, a[href*=javascript\:]:focus:after, a[onclick]:focus:after, fieldset > :not(legend):first-child:after, fieldset > legend:not(:first-child):after, label:not([for]):hover:after, *[accesskey]:hover:after, th:empty:hover:after, table > tr:only-child:after, table > tbody > tr:only-child:after, table[align]:after, table[bgcolor]:after, table[outline]:after, table[cellpadding]:after, table[cellspacing]:after, table[width]:after, td[width]:after, td[valign]:after {
    position: absolute;
    display: block;
    width: 200px;
    background: #fcfcfc;
    color: #333;
    outline: 2px solid;
    padding: 5px;
}

/* content styles */
applet:hover:after, basefont:hover:after, center:hover:after, dir:hover:after, font:hover:after, isindex:hover:after, menu:hover:after, strike:hover:after, s:hover:after, u:hover:after, *[background]:hover:after, *[bgcolor]:hover:after, *[clear]:hover:after, *[color]:hover:after, *[compact]:hover:after, *[noshade]:hover:after, *[nowrap]:hover:after, *[size]:hover:after, *[start]:hover:after, *[bottommargin]:hover:after, *[leftmargin]:hover:after, *[rightmargin]:hover:after, *[topmargin]:hover:after, *[marginheight]:hover:after, *[marginwidth]:hover:after, *[alink]:hover:after, *[link]:hover:after, *[text]:hover:after, *[vlink]:hover:after, *[align]:hover:after, *[valign]:hover:after, *[hspace]:hover:after, *[vspace]:hover:after, *[height]:hover:after, *[width]:hover:after, ul[type]:hover:after, ol[type]:hover:after, li[type]:hover:after, iframe:not([title]):hover:after {
    position: absolute;
    background: #fff;
    padding: 3px;
    outline: 2px solid;
    color: #333;
}

/* Deprecated Elements - cannot be overridden by user styles */
applet, basefont, center, dir, font, isindex, menu, s, strike, u {
    outline: 2px dotted red !important;
}

applet:hover:after {
    content: " <applet> is a deprecated HTML element";
}

basefont:hover:after {
    content: " <basefont> is a deprecated HTML element";
}

center:hover:after {
    content: " <center> is a deprecated HTML element";
}

dir:hover:after {
    content: " <dir> is a deprecated HTML element";
}

font:hover:after {
    content: " <font> is a deprecated HTML element";
}

isindex:hover:after {
    content: " <isindex> is a deprecated HTML element";
}

menu:hover:after {
    content: " <menu> is a deprecated HTML element";
}

strike:hover:after {
    content: " <strike> is a deprecated HTML element";
}

s:hover:after {
    content: " <s> is a deprecated HTML element";
}

u:hover:after {
    content: " <u> is a deprecated HTML element";
}

/* Deprecated Attributes - cannot be overridden by user styles */
*[background], *[bgcolor], *[clear], *[color], *[compact], *[noshade], *[nowrap], *[size], *[start], *[bottommargin], *[leftmargin], *[rightmargin], *[topmargin], *[marginheight], *[marginwidth], *[alink], *[link], *[text], *[vlink], *[align], *[valign], *[hspace], *[vspace], *[height], *[width], ul[type], ol[type], li[type] {
    outline: 2px solid red;
}

img[height], img[width] {
    outline: none;
}

*[background]:hover:after {
    content: " background is a deprecated HTML attribute";
}

*[bgcolor]:hover:after {
    content: " bgcolor is a deprecated HTML attribute";
}

*[clear]:hover:after {
    content: " clear is a deprecated HTML attribute";
}

*[color]:hover:after {
    content: " color is a deprecated HTML attribute";
}

*[compact]:hover:after {
    content: " compact is a deprecated HTML attribute";
}

*[noshade]:hover:after {
    content: " noshade is a deprecated HTML attribute";
}

*[nowrap]:hover:after {
    content: " nowrap is a deprecated HTML attribute";
}

*[size]:hover:after {
    content: " size is a deprecated HTML attribute";
}

*[start]:hover:after {
    content: " start is a deprecated HTML attribute";
}

*[bottommargin]:hover:after {
    content: " bottommargin is a deprecated HTML attribute";
}

*[leftmargin]:hover:after {
    content: " leftmargin is a deprecated HTML attribute";
}

*[rightmargin]:hover:after {
    content: " rightmargin is a deprecated HTML attribute";
}

*[topmargin]:hover:after {
    content: " topmargin is a deprecated HTML attribute";
}

*[marginheight]:hover:after {
    content: " marginheight is a deprecated HTML attribute";
}

*[marginwidth]:hover:after {
    content: " marginwidth is a deprecated HTML attribute";
}

*[alink]:hover:after {
    content: " alink is a deprecated HTML attribute";
}

*[link]:hover:after {
    content: " link is a deprecated HTML attribute";
}

*[text]:hover:after {
    content: " text is a deprecated HTML attribute";
}

*[vlink]:hover:after {
    content: " vlink is a deprecated HTML attribute";
}

*[align]:hover:after {
    content: " align is a deprecated HTML attribute";
}

*[valign]:hover:after {
    content: " valign is a deprecated HTML attribute";
}

*[hspace]:hover:after {
    content: " hspace is a deprecated HTML attribute";
}

*[vspace]:hover:after {
    content: " vspace is a deprecated HTML attribute";
}

*[height]:hover:after {
    content: " height is a deprecated HTML attribute";
}

*[width]:hover:after {
    content: " width is a deprecated HTML attribute";
}

ul[type]:hover:after, ol[type]:hover:after, li[type]:hover:after {
    content: " type is a deprecated HTML attribute";
}

/* Inline frames without title attribute */
iframe:not([title]) {
    outline: 2px solid red !important;
}

iframe:not([title]):hover:after {
    content: " <iframe> does not have a title attribute defined.";
}

/**
 *     Image-related checks
 *     Can't add generated content to images. Think...
 */

/* server-side image map. Yes these are sometimes still seen, if rarely */
img[ismap] {
    outline: 2px solid red;
}

/* Images without alt attribute */
img:not([alt]) {
    outline: 2px solid red;
}

/* something that has a role of image but no alternative */
div[role="img"]:not([aria-label]) {
    outline: 2px solid red;
}

/* I don't know if that will work; but worth a try. */
div[role="img"]:not([aria-label]):hover:after {
    content: " This content has a role of image but no aria-label attribute.";
}

/* images without a source */
img:not([src]),
img[src=""],
img[src="#"] {
    outline: 2px solid red !important;
}

/**
 *     Link-related checks
 */

/* Bad links, possibly relying on javascript to do something */
a[href=""], a[href="#"], a:not([href]), a[href*=javascript\:], a[onclick] {
    outline: 2px solid red !important;
}

a[href=""]:hover:after, a[href="#"]:hover:after, a:not([href]):hover:after, a[href*=javascript\:]:hover:after, a[onclick]:hover:after,
a[href=""]:focus:after, a[href="#"]:focus:after, a:not([href]):focus:after, a[href*=javascript\:]:focus:after, a[onclick]:focus:after {
    content: " This link may depend on JavaScript to perform it's function.";
}

/** 
 *     form-related checks
 */

/*
	Legends
*/
fieldset > :not(legend):first-child, /* no other element than a legend can be first child of a fieldset element */
fieldset > legend:not(:first-child) {
    /* and a legend can't be anything else than first child of a fieldset element */
    outline: 2px dashed red !important;
}

fieldset > :not(legend):first-child:after,
fieldset > legend:not(:first-child):after {
    content: " <legend> must be the first child of a fieldset";
}

/*
	Input[type="image"] and their alt attribute
	Note: adding :before or :after on this type of element won't work. Maybe background-image encoded in base64?
	@reference Technique for WCAG 2.0 H36: Using alt attributes on images used as submit buttons - http://www.w3.org/TR/WCAG-TECHS/H36.html
	@reference Technique for WCAG 2.0 F65: Failure (...) due to omitting the alt attribute on (...) input elements of type "image" - http://www.w3.org/TR/WCAG-TECHS/F65.html
*/
input[type="image"][alt=""],
input[type="image"]:not([alt]) {
    display: block;
    background-color: red !important;
    width: 200px !important;
    height: 3em !important;
}

/* Missing 'for' attribute on a label */
label:not([for]) {
    outline: 2px solid red !important;
}

label:not([for]):hover:after {
    content: " This label does not have a for attribute associating it with a form input.";
}

/* Accesskey is a bad idea. 
 * @reference Old discussion but still hits on salient points http://www.cs.tut.fi/~jkorpela/forms/accesskey.html */
*[accesskey] {
    outline: 2px solid red;
}

*[accesskey]:hover:after {
    content: " Do not use the accesskey attribute.";
}

/**
 *     TABLE RELATED CHECKS
 */

/* Empty Header Cells */
th:empty {
    padding: 20px;
    outline: 2px solid yellow !important;
}

th:empty:after {
    content: " Table header cell is empty.";
}

/* only one TR in the table. Is that a layout table? */
table > tr:only-child,
table > tbody > tr:only-child {
    outline: 2px solid red;
}

table > tr:only-child:after, table > tbody > tr:only-child:after {
    content: " Table has only one row. Is this a layout table?"
}

/* Deprecated attributes on table */
table[align],
table[bgcolor],
table[outline],
table[cellpadding],
table[cellspacing],
table[width],
td[width],
td[valign] {
    outline: 2px solid red;
}

table[align]:after,
table[bgcolor]:after,
table[outline]:after,
table[cellpadding]:after,
table[cellspacing]:after,
table[width]:after,
td[width]:after,
td[valign]:after {
    content: " This table uses one or more deprecated attributes: align, bgcolor, outline, cellpadding, cellspacing, width, or valign";
}