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.