body {
    font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
    display: flex;
    justify-content: center;
    align-items: center;
    height: 100vh;
    margin: 0;
    background-color: #121212; /* Dark theme background */
    color: #e0e0e0; /* Light text color */
    -webkit-tap-highlight-color: transparent;
}

#app {
    text-align: center;
    display: flex;
    flex-direction: column;
    justify-content: space-around; /* Adjusted for better spacing without bottom button */
    height: 90%;
    max-height: 600px; /* Limit height for larger screens */
    width: 90%;
    max-width: 400px; /* Limit width for larger screens */
    padding: 20px 0;
    box-sizing: border-box;
}

#timer {
    font-size: 2.8em; /* Slightly larger timer */
    font-weight: bold;
    color: #00bcd4; /* Accent color for timer */
    margin-bottom: 30px;
}

#circle {
    position: relative;
    width: 320px;
    height: 320px;
    border: 2px solid #555; /* Darker border for circle */
    border-radius: 50%;
    margin: 20px auto;
    display: flex;
    justify-content: center;
    align-items: center;
    background-color: #1e1e1e; /* Darker background for circle */
    box-shadow: 0 0 15px rgba(0, 0, 0, 0.5); /* More prominent shadow */
}

.number {
    position: absolute;
    font-size: 1.8em;
    width: 60px;
    height: 60px;
    line-height: 60px;
    text-align: center;
    color: #e0e0e0; /* Light text for numbers */
    font-weight: 500;
}

#center-container {
    display: flex;
    flex-direction: column; /* Allow sum and time to stack */
    justify-content: center;
    align-items: center;
    width: 130px; /* Slightly larger for results */
    height: 130px;
    border-radius: 50%;
    background-color: #2a2a2a; /* Darker background for center */
    box-shadow: 0 4px 10px rgba(0,0,0,0.3);
    transition: background-color 0.2s;
}

#center-container.new-circle-active {
    cursor: pointer;
    background-color: #2a2a2a; /* Can be slightly different for visual cue */
}

#center-container.new-circle-active:hover {
    background-color: #3a3a3a; /* Hover effect */
}

#done-button {
    width: 110px; /* Slightly larger done button */
    height: 110px;
    border-radius: 50%;
    font-size: 1.6em;
    font-weight: bold;
    cursor: pointer;
    border: none;
    background-color: #4CAF50;
    color: white;
    transition: background-color 0.2s;
}

#done-button:active {
    background-color: #45a049;
}

#result {
    font-size: 1.1em;
    text-align: center;
    color: #e0e0e0;
    font-weight: 500;
    line-height: 1.4;
    display: flex; /* Make result a flex container */
    flex-direction: column; /* Stack sum and time */
    justify-content: center;
    align-items: center;
    height: 100%; /* Ensure it fills center-container */
    width: 100%; /* Ensure it fills center-container */
}

#result .sum-value {
    font-size: 1.8em; /* Larger font for sum */
    color: #ffeb3b; /* Accent color for sum */
    display: block; /* Ensure it takes full width */
    margin-bottom: 5px;
}

#result .time-value {
    font-size: 1em; /* Smaller font for time */
    color: #9e9e9e; /* Muted color for time */
}

@media (max-width: 400px) {
    #app {
        height: 100%;
        width: 100%;
    }
    #circle {
        width: 280px;
        height: 280px;
    }
    .number {
        font-size: 1.5em;
        width: 50px;
        height: 50px;
        line-height: 50px;
    }
    #done-button {
        width: 90px;
        height: 90px;
        font-size: 1.4em;
    }
    #center-container {
        width: 100px;
        height: 100px;
    }
    #timer {
        font-size: 2.2em;
        margin-bottom: 20px;
    }
    #result .sum-value {
        font-size: 1.6em;
    }
    #result .time-value {
        font-size: 0.9em;
    }
}