使用html+css+js实现简易计算器

* {
    border: none;
    font-family: ‘Open Sans‘, sans-serif;
    margin: 0;
    padding: 0;
}

.calculator {
    background-color: #fff;
    height: 600px;
    margin: 50px auto;
    width: 600px;
}

form {
    background-color: rgb(75, 70, 71);
    padding: 5px 1px auto;    
    width: 245px;
}
.btn {
    outline: none;
    cursor: pointer;
    font-size: 20px;
    height: 45px;
    margin: 5px 0 5px 10px;
    width: 45px;
   
}
.btn:first-child {
    margin: 5px 0 5px 10px;
}

#display {
    outline: none;
    background-color: #dededc;
    color: rgb(75, 70, 71);
    font-size: 40px;
    height: 47px;
    text-align: right;
    width: 224px;
    margin: 10px 10px auto;
}
.number {
    background-color: rgb(143, 140, 140);
    color: #dededc;
}

.operator {
    background-color: rgb(239, 141, 49);
    color: #ffffff;
}

.equal{
    width: 105px;
}

.txt{
    font-size:12px;
    background: none;
}

/* display clear */ 
function cleardisplay() {
    document.getElementById("display").value = "";
}

/* del */
function del() {
    var numb = "";
    numb = document.getElementById("display").value;
    for(i=0;i