How can i customize search form like the format of html cut & css

i want customize the search form like the html cut & css :

form id="quick-search" action="index.html" method="get" >
<p>
	<label for="qsearch">Search:</label>
	<input class="tbox" id="qsearch" type="text" name="qsearch" title="Start typing and hit ENTER" />
	<input class="btn" alt="Search" type="image" name="searchsubmit" title="Search"     src="images/search.gif" />
</p>
</form>

i can change the value of form id='quick-search' into 'search_block_form' in css file. How about two fields input. How can i add class into them like the codes of file html cut.
How can i do that ? Can anyone help me solve this problem or give me some solutions ? Sorry about my English skill.