/* ===========================================
   1. 通用响应式底座 (所有样式均需依赖)
   =========================================== */
:root {
    --text-color: #333;
    --paper-bg: #fff;
    --wish-color: #333;
    --border-color: #ddd;
    --font-family-base: "Noto Serif SC", serif;
    --font-family-sig: "Noto Serif SC", serif; /* 默认署名字体 */
}

body {
    margin: 0;
    padding: 20px;
    background-color: #f6f6f6; /* 默认外背景 */
    font-family: var(--font-family-base);
    color: var(--text-color);
    display: flex;
    justify-content: center;
    transition: background 0.3s;
}

/* 自适应容器 */
.letter-container {
    width: 100%;
    max-width: 800px;
    min-height: 85vh;
    padding: 5% 7%;
    box-sizing: border-box;
    position: relative;
    box-shadow: 0 4px 15px rgba(0,0,0,0.05);
    background-color: var(--paper-bg);
    border: 1px solid var(--border-color);
    transition: all 0.3s ease;
}

/* 手机端适配 */
@media (max-width: 600px) {
    body { padding: 10px; }
    .letter-container { padding: 35px 20px; }
}

/* 传统书信格式公共逻辑 */
.salutation {
    font-size: 1.2rem;
    margin-top: 0;
    margin-bottom: 1.5rem;
    font-weight: bold;
}

.content p {
    text-indent: 2em; /* 首行缩进 */
    line-height: 1.8;
    text-align: justify;
    margin-bottom: 1rem;
}

.closing { margin-top: 2.5rem; }
.wish-prefix { text-indent: 2em; margin: 0; color: var(--wish-color); }
.wish-suffix { font-weight: bold; margin-top: 5px; color: var(--wish-color); }

.footer {
    text-align: right;
    margin-top: 4rem;
    line-height: 1.6;
}

.signature {
    font-size: 1.1em;
    font-family: var(--font-family-sig);
}

/* ===========================================
   2. 原始场景皮肤 (Modern, Traditional, Vintage)
   =========================================== */
/* ... (保留你之前的定义，此处略以节省空间，直接写新的) ... */
.theme-modern { --paper-bg: #fff; border-top: 4px solid #333; }
.theme-traditional { --paper-bg: #fdfaf2; writing-mode: vertical-rl; height: 650px; }
@media (max-width: 600px) { .theme-traditional { writing-mode: horizontal-tb; height: auto; } }
.theme-vintage { --paper-bg: #fff; border: 2px solid #b71c1c; background-image: repeating-linear-gradient(transparent, transparent 31px, rgba(183, 28, 28, 0.1) 31px, rgba(183, 28, 28, 0.1) 32px); line-height: 32px; --text-color: #b71c1c; --wish-color: #b71c1c; }


/* ===========================================
   3. [新增] 青春与多样场景皮肤
   =========================================== */

/* --- A. 青春派对 (Youthful) --- */
/* 特点：明亮多彩、活力、柔和 */
.theme-youth {
    --paper-bg: #fff;
    --text-color: #4a4a4a;
    --wish-color: #ff6b6b; /* 鲜艳的颜色 */
    --border-color: #ffe0e0;
    font-family: "PingFang SC", "Microsoft YaHei", sans-serif; /* 使用现代无衬线字体 */
    
    border-radius: 15px; /* 圆角增加亲和力 */
    border: 3px solid #ffe0e0;
}

/* 装饰：顶部和底部加点彩色条纹 */
.theme-youth::before {
    content: "";
    position: absolute;
    top: 0; left: 0; right: 0; height: 8px;
    background: linear-gradient(90deg, #ff6b6b, #feca57, #48dbfb, #ff9f43);
    border-radius: 15px 15px 0 0;
}

.theme-youth .salutation { color: #222; }
.theme-youth .content p { text-indent: 0; text-align: left; background-color: #fcfcfc; padding: 10px; border-radius: 8px; margin-bottom: 1.2rem; } /* 类似气泡感 */
.theme-youth .wish-prefix { text-indent: 0; padding-left: 1rem; } /* 青春风不一定强制缩进 */
.theme-youth .wish-suffix { font-weight: 800; font-size: 1.1rem; }
.theme-youth .footer { color: #888; }
.theme-youth .signature { color: #333; font-weight: bold; }


/* --- B. 青葱校园 (Campus) --- */
/* 特点：数学格子纸、怀旧、清爽蓝调 */
.theme-campus {
    --paper-bg: #fdfdfd;
    --text-color: #3e3e3e;
    --wish-color: #2980b9; /* 校园蓝 */
    --border-color: #87ceeb;
    font-family: "SimSun", serif; /* 怀旧宋体 */
    
    /* 模拟蓝格子纸 */
    background-image: 
        linear-gradient(rgba(135, 206, 235, 0.3) 1px, transparent 1px),
        linear-gradient(90deg, rgba(135, 206, 235, 0.3) 1px, transparent 1px);
    background-size: 25px 25px; /* 格子大小 */
}

/* 顶部加一个类似书签或校徽的圆 */
.theme-campus::after {
    content: "CAMPUS";
    position: absolute;
    top: -15px; right: 30px;
    background-color: #2980b9;
    color: white;
    padding: 5px 15px;
    border-radius: 20px;
    font-size: 0.8rem;
    font-family: sans-serif;
}

.theme-campus .content p { line-height: 1.6; text-indent: 2em; }
.theme-campus .closing { border-top: 1px dashed rgba(135, 206, 235, 0.5); padding-top: 1rem; }
.theme-campus .footer .date { color: #888; }


/* --- C. 极简和风 (Wabi-Sabi / Minimalist) --- */
/* 特点：淡雅、素净、极低对比度、高端商务或长辈 */
.theme-wabi {
    --paper-bg: #fafafa;
    --text-color: #555;
    --wish-color: #777;
    --border-color: transparent; /* 无边框 */
    font-family: "Source Han Serif SC", serif; /* 高质量宋体 */
    
    background-color: #fff;
    padding: 8% 10%; /* 更宽松的内边距 */
    border-radius: 0;
    box-shadow: none; /* 去掉阴影，极度扁平 */
}

/* 手机端去掉过于宽松的内边距 */
@media (max-width: 600px) {
    .theme-wabi { padding: 40px 20px; }
}

/* 装饰：只在底部加一条极淡的灰线 */
.theme-wabi .footer {
    text-align: right;
    border-top: 1px solid #f0f0f0;
    padding-top: 1.5rem;
}

.theme-wabi .salutation { font-weight: normal; font-size: 1.2rem; color: #333; }
.theme-wabi .content p { text-indent: 2em; line-height: 2; color: #666; font-size: 0.95rem; }
.theme-wabi .wish-suffix { font-weight: normal; color: #777; }
.theme-wabi .signature { font-family: "Zhi Mang Xing", cursive; font-size: 1.8rem; color: #333; } /* 使用Google Font书法字体 */