body {
    font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
    background-color: #f0f2f5;
    color: #333;
    line-height: 1.6;
    margin: 0;
    padding: 0;
}

.container {
    max-width: 1000px;
    margin: 20px auto;
    background: #fff;
    border-radius: 8px;
    box-shadow: 0 2px 8px rgba(0, 0, 0, 0.1);
    padding: 25px 35px;
}

h1 {
    color: #1a237e; /* 深蓝色 */
    text-align: center;
    margin-bottom: 10px;
    border-bottom: 2px solid #e8eaf6; /* 淡紫色 */
    padding-bottom: 10px;
}
h2 {
    color: #00695c; /* 青色 */
    margin-top: 25px;
    margin-bottom: 15px;
    font-size: 1.3em;
    text-align: center;
}

.back-link {
    display: inline-block;
    margin-bottom: 25px;
    color: #1976d2; /* 蓝色 */
    text-decoration: none;
    padding: 8px 15px;
    border: 1px solid #1976d2;
    border-radius: 5px;
    transition: background-color 0.3s, color 0.3s;
}

.back-link:hover {
    background-color: #1976d2;
    color: #fff;
}

.packet-display {
    margin-bottom: 30px;
}

.header-section {
    border: 2px solid #ccc;
    border-radius: 6px;
    margin-bottom: 25px;
    padding: 15px 20px;
    background-color: #f9f9f9;
}

.ethernet-header { border-color: #3498db; } /* 蓝色边框 */
.ip-header { border-color: #e67e22; }      /* 橙色边框 */
.tcp-header { border-color: #2ecc71; }      /* 绿色边框 */

.fields {
    display: flex;
    flex-wrap: wrap; /* Allow fields to wrap */
    border: 1px dashed #aaa;
    background-color: #fff;
    padding: 5px;
}

.field {
    border: 1px solid #bbb;
    padding: 8px 10px;
    margin: 3px;
    background-color: #e0e0e0; /* 浅灰色背景 */
    font-size: 0.85em;
    text-align: center;
    cursor: pointer;
    transition: background-color 0.2s, transform 0.2s;
    flex-grow: 1; /* Allow fields to grow */
    min-width: 60px; /* Minimum width for smaller fields */
    box-sizing: border-box; /* Include padding and border in width */
}

.field:hover {
    background-color: #f1c40f; /* 黄色高亮 */
    transform: scale(1.05);
    z-index: 10; /* Bring hovered element to front */
    box-shadow: 0 0 8px rgba(0,0,0,0.3);
}

/* Specific field styling */
.field.payload { background-color: #d1eaff; flex-basis: 100%; } /* 数据负载淡蓝色，占满一行 */
.field.options { background-color: #e8eaf6; flex-basis: 100%;} /* 选项淡紫色，占满一行 */
.field.wide { flex-basis: calc(100% - 10px); } /* 宽字段，几乎占满一行 */
.field.flags { background-color: #ffe0b2; } /* 标志位浅橙色 */
.field.reserved { background-color: #cfd8dc; color: #78909c; } /* 保留位灰色 */

/* Adjust flex basis for specific rows in IP/TCP headers if needed */
.ip-header .fields > .field:nth-child(-n+4) { flex-basis: calc(25% - 10px); } /* IP Row 1: 4 fields */
.ip-header .fields > .field:nth-child(n+5):nth-child(-n+7) { flex-basis: calc(33.33% - 10px); } /* IP Row 2: 3 fields (approx) */
.ip-header .fields > .field:nth-child(n+8):nth-child(-n+10) { flex-basis: calc(33.33% - 10px); } /* IP Row 3: 3 fields */

.tcp-header .fields > .field:nth-child(-n+2) { flex-basis: calc(50% - 10px); } /* TCP Row 1: 2 fields */
.tcp-header .fields > .field:nth-child(n+5):nth-child(-n+8) { flex-basis: calc(25% - 10px); } /* TCP Row 4: 4 fields */
.tcp-header .fields > .field:nth-child(n+9):nth-child(-n+10) { flex-basis: calc(50% - 10px); } /* TCP Row 5: 2 fields */


/* 新增 tooltip 样式 */
.tooltip {
    position: absolute; /* 相对于最近的定位祖先（或 body）*/
    display: none; /* 初始隐藏 */
    background-color: rgba(0, 0, 0, 0.75); /* 半透明黑色背景 */
    color: white;
    padding: 8px 12px;
    border-radius: 4px;
    font-size: 0.9em;
    white-space: nowrap; /* 防止内容换行 */
    z-index: 1000; /* 确保在最上层 */
    pointer-events: none; /* 允许鼠标事件穿透 tooltip */
    box-shadow: 0 2px 5px rgba(0,0,0,0.3);
    transition: opacity 0.1s ease-in-out; /* 可选：添加淡入效果 */
}

.tooltip p {
    margin: 4px 0;
    line-height: 1.4;
}
.tooltip strong {
    display: inline-block;
    width: 70px; /* 调整标签宽度 */
    color: #f1c40f; /* 黄色标签 */
    margin-right: 5px;
}


/* 新增：封装图示样式 */
.encapsulation-diagram {
    margin-top: 40px;
    padding-top: 20px;
    border-top: 2px solid #e0e0e0;
}

.encapsulation-diagram h2 {
    text-align: center;
    margin-bottom: 25px;
    color: #333;
}

.layer {
    border: 2px solid #aaa; /* Default border */
    margin: 5px;
    padding: 5px;
    position: relative; /* For label positioning */
    background-color: #f9f9f9;
    display: flex; /* Use flexbox for horizontal layout (header, payload, trailer) */
    flex-direction: row; /* Default row layout */
    align-items: stretch; /* Make children fill height */
    min-height: 60px; /* Ensure minimum height */
}

/* Nested layers should be block elements within the payload */
.layer-payload > .layer {
    display: block; /* Override flex for nested layers */
    width: auto; /* Allow nested layers to take available space */
    margin: 5px 0; /* Adjust margin for nested layers */
}

.layer-header, .layer-payload, .layer-trailer {
    padding: 20px 10px 10px 10px; /* Top padding for label */
    position: relative;
    border: 1px dashed #ccc; /* Dashed border for internal parts */
    margin: 2px;
    display: flex; /* Use flex for content alignment */
    align-items: center;
    justify-content: center;
    flex-direction: column; /* Stack label and content vertically */
}

.layer-header {
    min-width: 100px; /* Minimum width for headers */
    flex-shrink: 0; /* Prevent headers from shrinking */
    background-color: rgba(0, 0, 0, 0.03); /* Slightly different background */
}
.layer-payload {
    flex-grow: 1; /* Payload takes remaining space */
    min-height: 50px; /* Ensure payload has some height */
}
.layer-trailer {
     min-width: 60px;
     flex-shrink: 0;
     background-color: rgba(0, 0, 0, 0.03);
}

.layer-label {
    position: absolute;
    top: 2px;
    left: 5px;
    font-size: 0.8em; /* Smaller label */
    font-weight: bold;
    padding: 1px 4px;
    background-color: #fff;
    border: 1px solid #ccc;
    border-radius: 3px;
    z-index: 1; /* Ensure label is above background */
}
.layer-trailer .layer-label {
    left: auto;
    right: 5px;
}


/* --- Color Coding --- */

/* Ethernet Layer */
.layer-ethernet { border-color: #3498db; background-color: #eaf4fc; }
.ethernet-header-part { border-color: #3498db; }
.ethernet-header-part > .layer-label { color: #2980b9; border-color: #2980b9; }
.ethernet-trailer-part { border-color: #3498db; }
.ethernet-trailer-part > .layer-label { color: #2980b9; border-color: #2980b9; }

/* IP Layer */
.layer-ip { border-color: #e67e22; background-color: #fef5e7; }
.ip-header-part { border-color: #e67e22; }
.ip-header-part > .layer-label { color: #d35400; border-color: #d35400; }

/* TCP Layer */
.layer-tcp { border-color: #2ecc71; background-color: #eafaf1; }
.tcp-header-part { border-color: #2ecc71; }
.tcp-header-part > .layer-label { color: #27ae60; border-color: #27ae60; }

/* Data Layer */
.layer-data {
    border-color: #9b59b6;
    background-color: #f5eef8;
    border-style: solid; /* Solid border for data */
    text-align: center;
    color: #8e44ad;
    font-style: italic;
    min-height: 30px;
    padding: 20px 10px 10px 10px; /* Adjust padding */
    display: block; /* Override flex */
    margin: 5px 0;
}
.layer-data > .layer-label { color: #8e44ad; border-color: #8e44ad; }
.data-content {
    margin-top: 5px; /* Space between label and data text */
    font-size: 0.9em;
}

/* Adjust nested payload padding */
.layer-payload {
    padding: 5px; /* Reduce padding for payload areas containing other layers */
}
.layer-payload > .layer {
     margin: 0; /* Remove margin for directly nested layers */
}

/* --- 移除或注释掉之前的封装图示样式 --- */
/*
.encapsulation-diagram .layer { ... }
.layer-header, .layer-payload, .layer-trailer { ... }
.layer-label { ... }
.layer-ethernet, .layer-ip, .layer-tcp, .layer-data { ... }
.ethernet-header-part, .ip-header-part, .tcp-header-part, .ethernet-trailer-part { ... }
.data-content { ... }
*/

/* --- 新增：参照图片版的封装图示样式 --- */
.encapsulation-diagram.simple-diagram {
    margin-top: 30px; /* 可以稍微调整上边距 */
    /* padding-top: 20px; */ /* 移除单独的上内边距 */
    /* border-top: 2px solid #e0e0e0; */ /* 移除单独的上边框 */
    text-align: center; /* Center the title and diagram */
    border: 1px solid #ccc; /* 添加完整的边框 */
    padding: 20px; /* 在边框和内容之间添加内边距 */
    border-radius: 6px; /* 添加圆角 */
    background-color: #fdfdfd; /* 可以设置一个浅背景色 */
    margin-bottom: 30px; /* 增加下外边距，与下面的内容分隔开 */
}

.encapsulation-diagram.simple-diagram h2 {
    margin-bottom: 10px; /* Reduce bottom margin */
    margin-top: 0; /* 移除标题的上外边距，因为父元素有了内边距 */
}

.diagram-label {
    font-size: 1.1em;
    color: #555;
    margin-bottom: 15px;
    position: relative; /* For potential line drawing */
    display: inline-block; /* Fit content width */
    padding: 0 10px;
}

/* Optional: Add lines like in the image */
.diagram-label::before,
.diagram-label::after {
    content: '';
    position: absolute;
    top: 50%;
    width: 100px; /* Adjust width as needed */
    height: 1px;
    background-color: #888;
}
.diagram-label::before {
    right: 100%;
    margin-right: 10px;
}
.diagram-label::after {
    left: 100%;
    margin-left: 10px;
}


.frame-bar {
    display: flex; /* Arrange parts horizontally */
    width: 90%; /* Adjust overall width */
    margin: 0 auto; /* Center the bar */
    border: 1px solid #555;
    border-radius: 4px;
    overflow: hidden; /* Ensure rounded corners clip children */
    min-height: 50px; /* Minimum height */
}

.frame-part {
    padding: 10px 5px; /* Padding inside each part */
    color: white; /* Default text color */
    font-weight: bold;
    font-size: 0.9em;
    text-align: center;
    display: flex; /* Center content vertically */
    align-items: center;
    justify-content: center;
    border-right: 1px solid rgba(255, 255, 255, 0.3); /* Subtle separator */
    flex-grow: 1; /* Default: equal width */
    flex-basis: 0; /* Allow flex-grow to work properly */
}
.frame-part:last-child {
    border-right: none; /* No border on the last part */
}

/* --- Color Coding based on image --- */
.part-eth-header {
    background-color: #f39c12; /* Orange */
    flex-grow: 2; /* Make slightly wider */
}
.part-ip-header {
    background-color: #3498db; /* Blue */
    flex-grow: 1.5;
}
.part-tcp-header {
    background-color: #4fc3f7; /* Light Blue */
    flex-grow: 1.5;
}
.part-app-data {
    background-color: #b3e5fc; /* Lighter Blue */
    color: #333; /* Darker text for light background */
    flex-grow: 4; /* Make data section largest */
}
.part-fcs {
    background-color: #e67e22; /* Darker Orange */
    flex-grow: 1;
}