body {
    font-family: 'Arial', sans-serif;
    background: linear-gradient(120deg, #4a90e2, #c2e9fb); /* 从左上角到右下角，左边颜色更深 */
    display: flex;
    justify-content: center;
    align-items: center;
    height: 100vh;
    margin: 0;
}

.container {
    background: #fff;
    padding: 30px;
    border-radius: 20px;
    box-shadow: 0 10px 30px rgba(0, 0, 0, 0.2); /* 更深的阴影 */
    max-width: 400px;
    width: 100%;
    text-align: center;
}

h1 {
    margin-bottom: 20px;
    color: #333;
    font-size: 24px;
    font-weight: bold;
}

.input-group {
    margin: 20px 0;
    text-align: left;
}

.input-group label {
    display: block;
    margin-bottom: 10px;
    font-weight: bold;
    color: #555;
    font-size: 16px;
}

.input-group input {
    width: calc(100% - 22px);
    padding: 10px;
    margin-bottom: 10px;
    border: 1px solid #ccc;
    border-radius: 8px;
    box-shadow: inset 0 1px 3px rgba(0, 0, 0, 0.1);
    font-size: 16px;
    transition: border-color 0.3s, box-shadow 0.3s;
}

.input-group input:hover {
    box-shadow: 0 0 5px 2px rgba(0, 123, 255, 0.5); /* 悬停时的阴影效果 */
}

.input-group input:focus {
    border-color: #007BFF;
    outline: none;
    box-shadow: 0 0 5px 2px rgba(0, 123, 255, 0.5); /* 聚焦时的阴影效果 */
}

button {
    padding: 10px;
    margin-top: 10px;
    border: none;
    border-radius: 8px;
    background-color: #007BFF;
    color: white;
    cursor: pointer;
    width: 100%;
    font-size: 16px;
    transition: background-color 0.3s;
}

button:hover {
    background-color: #0056b3;
}

/* 新增的样式，用于无效输入的显示 */
.invalid-input {
    color: red;
    font-weight: bold;
}