Where is the custom file option?

I no longer see the “Custom file option”. I would like to have my own HTML style or change the current HTML5 styles. Is there any function that I can use to overwrite the current HTML5? I would like to change the below code.

Thanks in advance.

	case 'HTML5' :
		$htm['ul']		= ''; 
		$htm['ulc']		= ''; 
		$htm['li']		= '<span '; // required for rich snippets, microformat
		$htm['lic']		= '</span>';
		/* allow for a class specifictaion */
		$htm['row']		= '<article '; 	 // each event
		$htm['rowc'] 	= '</article>'.AMR_NL;
		$htm['hcell']	='<h2 '; 	// the 'column' header cell
		$htm['hcellc'] 	='</h2>';
		$htm['cell'] 	='';
		$htm['cellc'] 	='';
//
		$htm['grow']	= '<header><h3 ';	// the grouping html text for a group of events - not the surrounding selector
		$htm['growc']   = '</h3></header>'.AMR_NL;
		$htm['ghcell']  = '';
		$htm['ghcellc'] = '';
//
		$htm['head'] 	= '<h2 ';
		$htm['headc'] 	= '</h2>';
		$foot 	= '<div ';
		$htm['footc'] 	= '</div>';
//
		$htm['body'] 	= '<section ';	// the grouping html text for a group of events - not the surrounding selector
		$htm['bodyc'] 	= '</section>'.AMR_NL;
//
		$htm['box'] 	= '<section';  // the whole calendar
		$htm['boxc'] 	= '</section>'.AMR_NL;
		break;