border-bottom: 4px solid;
border: 1px solid #FFFFFF;
<table id="calculater" onClick="calculater()">
<td id="display" colspan="5" onClick="resultscalcaulte()">0</td>
<td class="numberkey" >1</td>
<td class="numberkey" >2</td>
<td class="numberkey" >3</td>
<td class="numberkey" >+</td>
<td class="numberkey" id="deletesign">c</td>
<td class="numberkey" >4</td>
<td class="numberkey" >5</td>
<td class="numberkey" >6</td>
<td class="numberkey" >-</td>
<td rowspan="3" id="equality" onclick="resultscalcaulte()">=</td>
<td class="numberkey" >7</td>
<td class="numberkey" >8</td>
<td class="numberkey" >7</td>
<td class="numberkey" >*</td>
<td class="numberkey" >+/-</td>
<td class="numberkey" >0</td>
<td class="numberkey" >.</td>
<td class="numberkey" >/</td>
<script type="text/javascript">
var re4=/.+[\+|-|\*|\/]{1,99}.+/
if (event.srcElement.innerText=="=") {
if (event.srcElement.innerText=="c") {
if (event.srcElement.id=="display") {
if (results.match(re1)) {
display.innerText="输入错误";
if(lastkey.match(re3)&&event.srcElement.innerText.match(re3)){
if(lastkey=="="&&event.srcElement.innerText.match(re3)){
if (event.srcElement.innerText=="+/-"&&results!="") {
results=String(results2);
display.innerText=results;
results = "-"+"("+results+")";
display.innerText=results;
results+=event.srcElement.innerText;
lastkey=event.srcElement.innerText;
display.innerText=results;
function resultscalcaulte(){
if (results.match(re1)||results.match(re2)) {
display.innerText="输入错误";
calresults=eval(results);
display.innerText=calresults;