Theme doesn't look right in Internet Explorer?

Hello everyone, I’m new to WordPress and this is the first blog I designed. The link is here: http://69.195.124.90/~tambeoco/ I’m using the free Semprul theme. I changed some of the appearance slightly in CSS just for the shadow around the main box to look stronger, along with changing the color of the navigation bar. Well all looks well in Firefox, Chrome, and Safari. However when looking at it in Internet Explorer it looks pretty bad. The shadow is taken off and the colors look dull. Also the widgets (such as the RSS Feed, Facebook, and Linkedin button) look like square instead of circles with no visually pleasing transitions when the mouse hovers over. I realize that Internet Explorer (version 8 or below) doesn’t support certain CSS or HTML5 capabilities, but is there any way to fix this in the code to make the it look close to how it should look like in other browsers? Also if anyone is on IE 9 or higher does it have that same look as IE 8 or below? I’m not an expert in CSS so if there’s places where I can add or re-edit it please be specific as possible. All the info and help would be much appreciated!