:root {
    --primary-color: #4a90e2;
    --secondary-color: #f2f2f2;
    --text-color: #333;
    --completed-color: #d9d9d9;
}

body {
    font-family: sans-serif;
    background-color: var(--secondary-color);
    color: var(--text-color);
    margin: 0;
    padding: 20px;
}

h1 {
    text-align: center;
    color: var(--primary-color);
}

.container {
    max-width: 600px;
    margin: 0 auto;
    background-color: #fff;
    padding: 20px;
    border-radius: 8px;
    box-shadow: 0 2px 4px rgba(0,0,0,0.1);
}

.form-container {
    display: flex;
    margin-bottom: 20px;
}

#month-select {
    padding: 10px;
    border-radius: 4px;
    border: 1px solid #ccc;
    margin-right: 10px;
}

#task-input {
    flex-grow: 1;
    padding: 10px;
    border-radius: 4px;
    border: 1px solid #ccc;
}

#add-task-btn {
    padding: 10px 15px;
    background-color: var(--primary-color);
    color: #fff;
    border: none;
    border-radius: 4px;
    cursor: pointer;
}

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

li {
    padding: 10px;
    border-bottom: 1px solid #eee;
    display: flex;
    justify-content: space-between;
    align-items: center;
}

li.completed {
    text-decoration: line-through;
    color: var(--completed-color);
}

.delete-btn {
    background-color: #e74c3c;
    color: #fff;
    border: none;
    padding: 5px 10px;
    border-radius: 4px;
    cursor: pointer;
}