body {
    font-family: -apple-system, system-ui, BlinkMacSystemFont, "Segoe UI", Helvetica, Arial, sans-serif, "Apple Color Emoji", "Segoe UI Emoji", "Segoe UI Symbol";
    font-size: 12pt;
    font-weight: normal;
    line-height: 31px;
    background: linear-gradient(-225deg, #69EACB 0%, #EACCF8 48%, #6654F1 100%);
}

ul {
    margin-top: 13px;
    margin-bottom: 13px;
}

li.liststylenone{
    list-style: none;
}

#box {
    width: 1100px;
    margin: 0 auto;
}

#header {
    height: auto;
    text-align: center;
    margin-top: 1em;
}

#nav {
    height: auto;
}

#maincontent {
    margin-top: 1em;
    margin-bottom: 8px;
    height: auto;
}

.clearfloat {
    clear: both;
}

#top_left {
    color: #743bfa;
    float: left;
    width: 532px;
    height: auto;
    border: 3px solid #743bfa;
    border-radius: 15px;
    background-color: rgba(250, 247, 255, 0.4);
}

#top_right {
    color: #743bfa;
    float: right;
    width: 532px;
    height: auto;
    border: 3px solid #743bfa;
    border-radius: 15px;
    background-color: rgba(250, 247, 255, 0.4);
}

.warning {
    color: #ff0000;
    margin-top: 1.15em;
    height: auto;
    border: 3px solid #ff3333;
    border-radius: 15px;
    background-color: rgba(255, 246, 246, 0.4);
    display: flex;
    justify-content: center;
}

#course {
    font-family: 'Courier New', Courier, monospace;
    font-weight:bold ;
    color: #007723;
    margin-top: 1.15em;
    height: auto;
    border: 3px solid #00a431;
    border-radius: 15px;
    background-color: rgba(246, 255, 249, 0.4);
}

#course_2rows {
    margin-top: 1.15em;
    height: auto;
}

#course_left {
    color: #007723;
    float: left;
    width: 532px;
    height: auto;
    border: 3px solid #00a431;
    border-radius: 15px;
    background-color: rgba(246, 255, 249, 0.4);
}

#course_right {
    color: #007723;
    float: right;
    width: 532px;
    height: auto;
    border: 3px solid #00a431;
    border-radius: 15px;
    background-color: rgba(246, 255, 249, 0.4);
}

#reference {
    color: #e19805;
    margin-top: 1.15em;
    height: auto;
    border: 3px solid #e19805;
    border-radius: 15px;
    background-color: rgba(240, 240, 231, 0.4);
}



/* 
    a:hover 必须被置于 a:link 和 a:visited 之后，才是有效的。
    a:active 必须被置于 a:hover 之后，才是有效的。
    link -> visited -> hover -> active
*/
a.top_left_a:link,
a.top_left_a:visited {
    color: #0000FF;
    text-decoration: none;
}
a.top_left_a:hover {
    color: #0000FF;
    border-bottom: 2px dotted #743bfa;
    padding-bottom: 2px;
}


a.top_right_a:link,
a.top_right_a:visited {
    color: #0000FF;
    text-decoration: none;
}
a.top_right_a:hover {
    color: #0000FF;
    border-bottom: 2px dotted #743bfa;
    padding-bottom: 2px;
}


a.warning_a:link,
a.warning_a:visited {
    color: #ff0000;
    text-align: center;
    padding: 6px 26px;
    text-decoration: none;
}
a.warning_a:hover {
    color: #fff;
    background-color: #ff0000;
}


a.course_a:link,
a.course_a:visited {
    font-family: -apple-system,
        system-ui,
        BlinkMacSystemFont,
        "Segoe UI",
        Helvetica,
        Arial,
        sans-serif,
        "Apple Color Emoji",
        "Segoe UI Emoji",
        "Segoe UI Symbol";
    font-weight: normal;
    color: #0000FF;
    text-decoration: none;
}
a.course_a:hover {
    font-family: -apple-system, system-ui, BlinkMacSystemFont, "Segoe UI", Helvetica, Arial, sans-serif, "Apple Color Emoji", "Segoe UI Emoji", "Segoe UI Symbol";
    font-weight: normal;
    color: #0000FF;
    border-bottom: 2px dotted #00a431;
    padding-bottom: 2px;
}


a.reference_a:link,
a.reference_a:visited {
    color: #0000FF;
    border-radius: 5px;
    padding-left: 6px;
    padding-right: 6px;
    margin-right: 6px;
    text-decoration: none;
}
a.reference_a:hover {
    color: #ffffff;
    background-color: #d78f00;
    border-radius: 5px;
    padding-left: 6px;
    padding-right: 6px;
    margin-right: 6px;
}