style.css

body {
    margin: 0;
    font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, Oxygen, 
        Ubuntu, Cantarell, 'Open Sans', 'Helvetica Neue', sans-serif;
}

input, textarea {
    transition: border-color 0.2s;
}

input:focus, textarea:focus {
    outline: none;
    border-color: #3b82f6;
    box-shadow: 0 0 0 1px #3b82f6;
}

button {
    transition: background-color 0.2s;
    cursor: pointer;
}