* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
}

body {
    font-family: Arial, sans-serif;
    background-color: #f5f5f5;
    color: #333;
    padding-bottom: 110px;
}

header {
    background-color: #212529;
    color: white;
    padding: 20px;
    text-align: center;
}

.main-section {
    display: flex;
    min-height: 250px;
    margin: 20px;
    gap: 20px;
}

.left-panel,
.center-panel,
.right-panel {
    flex: 1;
    background-color: white;
    padding: 20px;
    border-radius: 8px;
    box-shadow: 0 2px 10px rgba(0,0,0,0.1);
    min-height: 250px;
}

.left-panel h2,
.center-panel h2,
.right-panel h2 {
    color: #2c3e50;
    margin-bottom: 15px;
    border-bottom: 2px solid #3498db;
    padding-bottom: 5px;
}

.left-panel ul {
    list-style-type: none;
    padding-left: 0;
}

.left-panel li {
    margin-bottom: 8px;
    padding: 5px;
    background-color: #ecf0f1;
    border-left: 4px solid #3498db;
    padding-left: 10px;
}

.input-group {
    display: flex;
    margin-bottom: 10px;
    align-items: center;
}

.number-input {
    flex: 1;
    padding: 10px;
    border: 2px solid #bdc3c7;
    border-radius: 4px;
    font-size: 16px;
    margin-right: 10px;
}

.number-input:focus {
    border-color: #3498db;
    outline: none;
}

.number-input.error {
    border-color: #e74c3c;
    background-color: #fdf2f2;
}

.remove-btn {
    background-color: #e74c3c;
    color: white;
    border: none;
    padding: 10px 15px;
    border-radius: 4px;
    cursor: pointer;
    font-size: 16px;
    font-weight: bold;
}

.remove-btn:hover {
    background-color: #c0392b;
}

.remove-btn:disabled {
    background-color: #bdc3c7;
    cursor: not-allowed;
}

.control-buttons {
    margin-top: 20px;
    display: flex;
    gap: 10px;
}

#add-btn,
#calculate-btn {
    padding: 12px 20px;
    border: none;
    border-radius: 4px;
    cursor: pointer;
    font-size: 16px;
    font-weight: bold;
}

#add-btn {
    background-color: #27ae60;
    color: white;
}

#add-btn:hover {
    background-color: #229954;
}

#add-btn:disabled {
    background-color: #bdc3c7;
    cursor: not-allowed;
}

#calculate-btn {
    background-color: #3498db;
    color: white;
}

#calculate-btn:hover {
    background-color: #2980b9;
}

#result-container {
    display: flex;
    flex-direction: column;
    justify-content: center;
    align-items: center;
    height: 200px;
    text-align: center;
}

#numeric-result {
    font-size: 24px;
    font-weight: bold;
    color: #2c3e50;
    margin-bottom: 15px;
}

#text-result {
    font-size: 16px;
    color: #7f8c8d;
    font-style: italic;
    line-height: 1.4;
}

footer {
    background-color: #212529;
    position: fixed;
    bottom: 0;
    left: 0;
    width: 100%;
    height: 100px;
    text-align: center;
    color: aliceblue;
    font-size: 1.25 rem;
    font-family: 'Arial';
    display: flex;
    justify-content: center;
    align-items: center;
}


@media (max-width: 768px) {
    .main-section {
        flex-direction: column;
    }
    
    .control-buttons {
        flex-direction: column;
    }
}