/* 基础样式 */
body {
    margin: 0;
    padding: 0;
    line-height: 1.6;
    color: #333;
}

.header {
    padding: 20px;
    background-color: #f8f9fa;
    text-align: center;
    opacity: 0.9;
    display: flex;
    align-items: center;
    justify-content: space-between; /* 修改为两端对齐 */
    border-bottom: 2px solid #2196F3;
}

.background-content {
    position: relative;
    background-color: #E3F2FD;
    margin: 10px 5%;
    opacity: 0.92;
    border-radius: 20px;
    border: 2px solid #2196F3; /* 增加亮蓝色描边 */
    padding: 0; /* 保持内容区间距由子元素控制 */
}

.footer-copyright {
    width: 100%;
    box-sizing: border-box;
    background: #e3f2fd;
    color: #1769aa;
    font-size: 0.98rem;
    text-align: center;
    padding: 14px 0 12px 0;
    border-top: 1.5px solid #2196F3;
    border-radius: 0 0 18px 18px;
    margin-top: 18px;
    line-height: 1.8;
}

.beian-info {
    display: inline-block;
    margin-top: 4px;
    font-size: 0.96rem;
    color: #1976d2;
    background: #fff;
    border-radius: 6px;
    padding: 2px 10px;
    box-shadow: 0 1px 4px 0 rgba(33,150,243,0.06);
}

.beian-info a {
    color: #2196F3;
    text-decoration: none;
    margin: 0 4px;
    transition: color 0.2s;
}

.beian-info a:hover {
    color: #1565c0;
    text-decoration: underline;
}

.beian-split {
    color: #90caf9;
    margin: 0 6px;
}

.header > div {
    margin-left: 5%;
    font-size: 2rem;
    font-weight: bold;
    letter-spacing: 4px;
    color: #1769aa;
    background: linear-gradient(90deg, #2196F3 30%, #00BCD4 70%);
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    background-clip: text;
    text-shadow: 0 2px 12px rgba(33,150,243,0.10);
    margin-right: 18px;
    user-select: none;
    transition: color 0.2s;
}

.btn {
    margin-right: 5%;
    background: linear-gradient(90deg, #2196F3 60%, #00BCD4 100%);
    color: #fff;
    font-size: 1.08rem;
    font-weight: 600;
    border: none;
    border-radius: 8px;
    padding: 8px 28px;
    margin-left: 18px;
    box-shadow: 0 2px 8px 0 rgba(33,150,243,0.10);
    cursor: pointer;
    letter-spacing: 2px;
    transition: background 0.2s, box-shadow 0.2s, transform 0.15s;
}

.btn:hover {
    background: linear-gradient(90deg, #1769aa 60%, #00BCD4 100%);
    box-shadow: 0 4px 16px 0 rgba(33,150,243,0.18);
    transform: translateY(-2px) scale(1.04);
}

.main-content {
    display: flex;
    justify-content: center;
    align-items: center;
    padding: 0;
}

.intro {
    border-radius: 18px;
    padding: 6px 48px 32px 48px;
    text-align: center;
    margin: 0;
}

.intro h1 {
    font-size: 2.4rem;
    font-weight: 800;
    margin-bottom: 18px;
    letter-spacing: 2px;
    background: linear-gradient(90deg, #2196F3 20%, #00BCD4 60%, #c4dff2 100%);
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    background-clip: text;
    text-shadow: 0 4px 16px rgba(33,150,243,0.12);
}

.intro h2 {
    font-size: 1.4rem;
    font-weight: 600;
    margin-bottom: 16px;
    letter-spacing: 1px;
    background: linear-gradient(90deg, #00BCD4 10%, #2196F3 80%);
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    background-clip: text;
    background-clip: text;
    text-shadow: 0 2px 8px rgba(0,188,212,0.10);
}

/* 移动端适配 */
@media (max-width: 768px) {
    .main-content {
        padding: 20px 0 0 0;
    }
    .intro {
        padding: 20px 10px 18px 10px;
        max-width: 98vw;
    }
    .intro h1 {
        font-size: 1.4rem;
    }
    .intro h2 {
        font-size: 1rem;
    }
}

.letter-ui {
    margin: 32px 10% 0 10%;
    background: #fff;
    border-radius: 14px;
    box-shadow: 0 4px 24px 0 rgba(33,150,243,0.10);
    border: 1.5px solid #E3F2FD;
    padding: 28px 32px 22px 32px;
    font-family: 'STKaiti', 'KaiTi', 'Microsoft YaHei', serif;
    color: #333;
    position: relative;
    letter-spacing: 1px;
    line-height: 2;
}

.letter-header {
    font-size: 1.7rem;
    color: #1769aa;
    margin-bottom: 18px;
    font-weight: 600;
}

.letter-to {
    font-weight: 700;
    color: #2196F3;
    margin-left: 6px;
}

.letter-body {
    font-size: 1.5rem;
    margin-bottom: 24px;
    white-space: pre-line;
}

.letter-footer {
    text-align: right;
    color: #1976d2;
    font-size: 1.7rem;
    font-weight: 600;
    letter-spacing: 2px;
}

@media (max-width: 768px) {
    .letter-ui {
        margin: 32px 5% 0 5%;
        padding: 16px 8px 12px 8px;
        font-size: 0.98rem;
    }
    .letter-body {
    font-size: 1rem;
    }
    .letter-header {
        font-size: 1rem;
        margin-bottom: 12px;
    }
    .letter-footer {
        font-size: 0.96rem;
    }
}