style.css

* {
    box-sizing: border-box;
}

body {
    display: grid;
    place-content: center;
    min-height: 100vh;
    margin: 0;
}

main {
    width: min(95vw, 400px);
}

h2 {
    text-align: center;
    color: rgb(36, 36, 36);
}

textarea {
    width: 100%;
    min-height: 150px;
    padding: 10px;
    border-color: #ccc;
    border-radius: 5px;
    outline-color: #ccc;
    line-height: 1.5;
}

div {
    display: flex;
    justify-content: space-evenly;
}

button {
    width: 100px;
    height: 30px;
    border-radius: 5px;
    border: none;
    background-color: #4CAF50;
    color: white;
    font-size: 15px;
    cursor: pointer;
}

button#stopBtn {
    background-color: #f44336;
}

#startBtn.listening {
    animation: pulse 2s infinite;
}

@keyframes pulse {
    0% {
        transform: scale(1);
    }

    50% {
        transform: scale(1.1);
    }

    100% {
        transform: scale(1);
    }
}