Why submit button is italic?

<input type="submit" value="SEA">

css

input[type="submit"]{
    display:block;
    margin:0 auto;
    padding:0 25px;
    cursor:pointer;
    font-weight:bold;
    letter-spacing:0.5px;
    color:#ffffff;
    text-shadow:-1px 1px #000000;
    line-height:27px;
    background-image:url(backs/01.png);
    border:0;
    border-radius:5px;
    outline:none;
    font-style:normal;
}

The text SEA is in italic letters. How to set normal letters on the button?