The DOM includes a frames collection you can access with JavaScript:
You'd need a name attribute on your iframe tag
<iframe name = "myFrame"
width="340" scrolling="no" height="37"
src="http://www.indiansplash.com/business/include/dash11i.php"
id="ifr" hspace="0" marginwidth="0" marginheight="0" vspace="0"
style="width: 585px; height: 47px; border: #dddddd 1px solid">
</iframe>
Then you can access it like this:
var myFrame = frames["myFrame"]
You can apply a new stylesheet to the content by following the example here: How to apply CSS to iframe?
UPDATE
Following the example in the reference i cited above:
var cssLink = document.createElement("link")
cssLink.href = "iframeStyles.css"; /* change this to the url for a stylesheet targetting the iframe */
cssLink .rel = "stylesheet";
cssLink .type = "text/css";
frames['myFrame'].document.body.appendChild(cssLink);
Then in iframeStyles.css
:
td{border:1px solid red;} /*or whatever*/
You may need a selector with stronger specificity, or apply !important to styles to overide already existing declarations.