body {
    font-family: Arial, sans-serif;
    text-align: center;
    margin: 20px;
    background-color: #f5f5f5;
}

h1 {
    font-size: 32px;
    color: #333;
}

#timer-display {
    font-size: 48px;
    font-weight: bold;
    color: #333;
    margin: 20px 0;
}

#controls {
    margin: 20px 0;
}

button {
    padding: 10px 20px;
    margin: 0 5px;
    font-size: 16px;
    cursor: pointer;
    border: none;
    border-radius: 5px;
}

#start-btn { 
    background-color: #4CAF50; 
    color: white; 
}

#pause-btn { 
    background-color: #FFC107; 
    color: white; 
}

#reset-btn { 
    background-color: #F44336; 
    color: white; 
}

button:hover {
    opacity: 0.9;
}

button:disabled {
    opacity: 0.5;
    cursor: not-allowed;
}

#session-history {
    margin-top: 20px;
}

#session-list {
    list-style-type: none;
    padding: 0;
}

#session-list li {
    padding: 5px 0;
    font-size: 14px;
}