:root {
    --background-color: #f4f7f9;
    --container-bg: #ffffff;
    --primary-color: #4a90e2;
    --text-color: #333;
    --subtle-text-color: #888;
    --border-color: #e0e0e0;
    --shadow-color: rgba(0, 0, 0, 0.1);
    --completed-color: #9b9b9b;
}

body {
    /*font-family: 'Noto Sans SC', sans-serif;*/
    font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", "Microsoft YaHei", "PingFang SC", "Hiragino Sans GB", "Helvetica Neue", Helvetica, Arial, sans-serif;
    background-color: var(--background-color);
    margin: 0;
    padding: 0;
    display: flex;
    justify-content: center;
    align-items: center;
    min-height: 100vh;
    color: var(--text-color);
}

.container {
    background-color: var(--container-bg);
    border-radius: 12px;
    box-shadow: 0 8px 30px var(--shadow-color);
    width: 100%;
    max-width: 500px;
    padding: 40px;
    box-sizing: border-box;
    transition: all 0.3s ease;
}

/* 登录界面 */
#login-screen {
    text-align: center;
}

#login-screen h1 {
    font-size: 2em;
    font-weight: 700;
    margin-bottom: 10px;
}

#login-screen p {
    color: var(--subtle-text-color);
    margin-bottom: 30px;
}

#email-input {
    width: 100%;
    padding: 15px;
    border: 1px solid var(--border-color);
    border-radius: 8px;
    font-size: 1em;
    box-sizing: border-box;
    margin-bottom: 20px;
    transition: border-color 0.3s;
}

#email-input:focus {
    outline: none;
    border-color: var(--primary-color);
}

#login-btn {
    width: 100%;
    padding: 15px;
    background-color: var(--primary-color);
    color: white;
    border: none;
    border-radius: 8px;
    font-size: 1.1em;
    font-weight: 500;
    cursor: pointer;
    transition: background-color 0.3s;
}

#login-btn:hover {
    background-color: #357abd;
}


/* Todo 应用界面 */
.hidden {
    display: none;
}

header {
    border-bottom: 1px solid var(--border-color);
    padding-bottom: 20px;
    margin-bottom: 20px;
}

.user-info {
    display: flex;
    justify-content: space-between;
    align-items: center;
    margin-bottom: 20px;
    color: var(--subtle-text-color);
    font-size: 0.9em;
}

#logout-btn {
    background: none;
    border: 1px solid var(--border-color);
    color: var(--subtle-text-color);
    padding: 5px 10px;
    border-radius: 5px;
    cursor: pointer;
    transition: all 0.3s;
}

#logout-btn:hover {
    background-color: #f1f1f1;
    color: var(--text-color);
}

header h1 {
    text-align: center;
    font-size: 2.5em;
    font-weight: 700;
    margin: 0;
}

#new-todo-form {
    display: flex;
    margin-top: 20px;
}

#new-todo-input {
    flex-grow: 1;
    padding: 15px;
    border: 1px solid var(--border-color);
    border-radius: 8px 0 0 8px;
    font-size: 1em;
    outline: none;
    transition: border-color 0.3s;
}

#new-todo-input:focus {
    border-color: var(--primary-color);
}

#new-todo-form button {
    padding: 15px 20px;
    font-size: 1.5em;
    background-color: var(--primary-color);
    color: white;
    border: none;
    border-radius: 0 8px 8px 0;
    cursor: pointer;
    transition: background-color 0.3s;
}

#new-todo-form button:hover {
    background-color: #357abd;
}

main {
    max-height: 40vh;
    overflow-y: auto;
}

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

.todo-item {
    display: flex;
    align-items: center;
    padding: 15px 5px;
    border-bottom: 1px solid var(--border-color);
    transition: background-color 0.2s;
}

.todo-item:last-child {
    border-bottom: none;
}

.todo-item:hover {
    background-color: #fafafa;
}

.todo-item .checkbox {
    width: 20px;
    height: 20px;
    border-radius: 50%;
    border: 2px solid var(--border-color);
    cursor: pointer;
    margin-right: 15px;
    flex-shrink: 0;
    display: flex;
    align-items: center;
    justify-content: center;
    transition: all 0.3s;
}

.todo-item.completed .checkbox {
    background-color: var(--primary-color);
    border-color: var(--primary-color);
}

.todo-item.completed .checkbox::after {
    content: '✔';
    color: white;
    font-size: 14px;
}

.todo-item .content {
    flex-grow: 1;
    transition: color 0.3s;
}

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

.todo-item .delete-btn {
    background: none;
    border: none;
    color: var(--subtle-text-color);
    font-size: 1.2em;
    cursor: pointer;
    opacity: 0;
    transition: opacity 0.3s;
}

.todo-item:hover .delete-btn {
    opacity: 1;
}

footer {
    text-align: center;
    margin-top: 30px;
    font-size: 0.8em;
    color: var(--subtle-text-color);
}

footer a {
    color: var(--primary-color);
    text-decoration: none;

}