body {
    font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, "Helvetica Neue", Arial, sans-serif;
    display: flex;
    justify-content: center;
    align-items: center;
    min-height: 100vh;
    margin: 0;
    background-color: #f4f7f6;
    color: #333;
}

.container {
    text-align: center;
    background-color: #ffffff;
    padding: 40px;
    border-radius: 8px;
    box-shadow: 0 4px 12px rgba(0, 0, 0, 0.1);
}

h1 {
    font-size: 2em;
    margin-bottom: 0.5em;
}

p {
    font-size: 1.1em;
    color: #666;
    margin-bottom: 2em;
}

#heartbeatBtn {
    font-size: 1.5em;
    font-weight: bold;
    color: #ffffff;
    background-color: #28a745; /* A reassuring green */
    border: none;
    padding: 15px 30px;
    border-radius: 5px;
    cursor: pointer;
    transition: background-color 0.3s ease, transform 0.1s ease;
}

#heartbeatBtn:hover {
    background-color: #218838;
}

#heartbeatBtn:active {
    transform: scale(0.98);
}

#heartbeatBtn:disabled {
    background-color: #94d3a2;
    cursor: not-allowed;
}

#status {
    margin-top: 1.5em;
    font-size: 1em;
    min-height: 1.2em; /* Reserve space to prevent layout shift */
    font-weight: bold;
}