textarea {
    width: 100%;
    margin: 8px 0;
    box-sizing: border-box;
    border: none;
    border-bottom: 2px solid black;
}

    textarea:focus {
        border-color: black;
        outline: none;
        border-bottom: 1px solid black;
    }

    textarea:Hover:not(:focus) {
        border-color: black;
        outline: none;
        border-bottom: 3px solid black;
    }