Remove all stylings (border, glow) from textarea

The glow effect is most-likely controlled by box-shadow. In addition to adding what Pavel said, you can add the box-shadow property for the different browser engines.

textarea {
    border: none;
    overflow: auto;
    outline: none;

    -webkit-box-shadow: none;
    -moz-box-shadow: none;
    box-shadow: none;

    resize: none; /*remove the resize handle on the bottom right*/
}

You may also try adding !important to prioritize this CSS.