* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
}

html, body {
    height: 100%;
    margin: 0;
}

body {
    display: flex;
    flex-direction: column;
    /* 让 body 成为纵向 flex 容器 */
}

.topClass {
    height: 90px;
    flex-shrink: 0;          /* 防止被压缩 */
    background-image: url("../img/header_bg.jpg");
    background-size: cover;
    background-position: center;
    font-size: 2em;
}

/* 中间内容区：撑满剩余高度 */
.content {
    flex: 1;                 /* 关键：占满剩余空间 */
    display: flex;           /* 内部左右布局 */
    overflow: hidden;        /* 防止溢出 */
}

.leftClass {
    background-color: #ece693;
    width: 10%;
    padding-top: 10px;
    /* 不用再写固定 height，flex 会自动撑满 */
}

.mainClass {
    background-color: #bdffff;
    width: 90%;
    /* 同样不用写固定 height */
}

.bottomClass {
    height: 50px;
    flex-shrink: 0;
    background-color: #e6de9b;
}

/* 清除浮动（关键！） */
.clearfix::after {
    content: "";
    display: block;
    clear: both;
}

/* 一级按钮样式 */
.a_levelOne{
	display:inline-block;
	height: 60px;
	margin:15px 30px;
	text-decoration:none;
	font-weight:bold;
	color:blue;
}

a.a_levelOne:hover{
	background-color:#00ff40;
}

.a_active {
	color: #ff0e00;
}

/* 二级按钮样式*/
.a_levelTwo{
	text-decoration:none;
	display:block;
	width:90%;
	margin-left:15px;
	margin:10px 5px;
	font-size:22px;
	font-weight:bold;
	text-align:left;
	color:blue;
}

a.a_levelTwo:hover{
	background-color:#5efb55;
}

.a_active2 {
	color: #e180cc;
}

/* 三级菜单按钮样式 */
.a_levelThree{
	text-decoration:none;
	display:block;
	width:90%;
	margin-right:15px;
	margin-bottom:8px;
	color:red;
	font-size:14px;
	font-weight:bold;
	text-align:right;
}

.ATagClass2{
	display:block;
	backgroud:#f1f1f1;
	width:90%;
	height:40px;
	padding:2px 0;
	font-size:16px;
	font-color:#8080ff;
	font-weight:bold;
	text-align:center;
}

/* 统一按钮样式 */
input[type="button"]{
	background-color:#00ff40;
	font-size:16px;
	font-weight:bold;
	padding:5px 10px;
	border:solid #001bff 1px;
	border-radius:4px; 
}

input[type="reset"]{
	background-color: #d9e7e5;
	font-size:16px;
	font-weight:bold;
	color:#4fcfdd;
	padding:5px 10px;
	border:solid #00ffe0 1px;
	border-radius:4px;

}

select{
    height:1.5em;
}

/* 网页标题样式 */
.titleA_style{
	display:inline-block;
	text-decoration:none;
	text-align:center;
	margin:0 5px;
	padding:0 5px;
	border:dotted blue 1px;
	font-size:1.5em;
	color:green;
}