移除HTML5 input在type="number"时的上下小箭头

Chrome

input::-webkit-outer-spin-button,
input::-webkit-inner-spin-button {
    -webkit-appearance: none;
    margin: 0;
}

FireFox

input[type='number'] {
    -moz-appearance:textfield;
}

参考：https://stackoverflow.com/questions/3790935/can-i-hide-the-html5-number-input-s-spin-box