:root {
    --bg-color: #f4f4f4;
    --text-color: #333;
    --app-bg: #fff;
    --app-shadow: rgba(0, 0, 0, 0.1);
    --border-color: #ccc;
    --li-border: #eee;
    --completed-color: #aaa;
}

body.dark-mode {
    --bg-color: #1a1a1a;
    --text-color: #f4f4f4;
    --app-bg: #2d2d2d;
    --app-shadow: rgba(0, 0, 0, 0.5);
    --border-color: #444;
    --li-border: #444;
    --completed-color: #777;
}

body {
    font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
    background-color: var(--bg-color);
    color: var(--text-color);
    display: flex;
    justify-content: center;
    align-items: center;
    min-height: 100vh;
    margin: 0;
    transition: background-color 0.3s, color 0.3s;
}

#app {
    background-color: var(--app-bg);
    border-radius: 8px;
    box-shadow: 0 4px 6px var(--app-shadow);
    padding: 2rem;
    width: 90%;
    max-width: 400px;
    position: relative;
    transition: background-color 0.3s, box-shadow 0.3s;
}

h1 {
    text-align: center;
    margin-top: 0;
}

#theme-toggle {
    position: absolute;
    top: 1rem;
    right: 1rem;
    background: none;
    border: none;
    font-size: 1.5rem;
    cursor: pointer;
    padding: 0;
}

#add-todo-form {
    display: flex;
    gap: 0.5rem;
    margin-bottom: 1.5rem;
}

#new-todo-input {
    flex: 1;
    padding: 0.6rem;
    border: 1px solid var(--border-color);
    border-radius: 4px;
    background-color: var(--app-bg);
    color: var(--text-color);
}

button[type="submit"] {
    padding: 0.6rem 1.2rem;
    background-color: #007bff;
    color: white;
    border: none;
    border-radius: 4px;
    cursor: pointer;
    font-weight: bold;
}

button[type="submit"]:hover {
    background-color: #0056b3;
}

#todo-list {
    list-style: none;
    padding: 0;
    margin: 0;
}

li {
    display: flex;
    align-items: center;
    padding: 0.75rem 0;
    border-bottom: 1px solid var(--li-border);
}

li:last-child {
    border-bottom: none;
}

.todo-text {
    flex: 1;
    cursor: pointer;
}

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

.delete-btn {
    background-color: #ff4d4d;
    color: white;
    border: none;
    border-radius: 4px;
    padding: 0.4rem 0.8rem;
    cursor: pointer;
    font-size: 0.8rem;
    margin-left: 1rem;
}

.delete-btn:hover {
    background-color: #cc0000;
}

hr {
    margin: 2rem 0;
    border: 0;
    border-top: 1px solid var(--li-border);
}

#partnership-section h2 {
    text-align: center;
    font-size: 1.2rem;
    margin-bottom: 1rem;
}

.form-group {
    margin-bottom: 1rem;
    display: flex;
    flex-direction: column;
    gap: 0.3rem;
}

.form-group label {
    font-size: 0.9rem;
    font-weight: bold;
}

.form-group input, 
.form-group textarea {
    padding: 0.6rem;
    border: 1px solid var(--border-color);
    border-radius: 4px;
    background-color: var(--app-bg);
    color: var(--text-color);
    font-family: inherit;
}

.submit-btn {
    width: 100%;
    padding: 0.75rem;
    background-color: #28a745;
    color: white;
    border: none;
    border-radius: 4px;
    cursor: pointer;
    font-weight: bold;
    font-size: 1rem;
    transition: background-color 0.2s;
}

.submit-btn:hover {
    background-color: #218838;
}