/* ============================================================
   作业提交系统 样式表（浅色主题）
   ============================================================ */
:root {
    --bg: #f4f6fb;
    --card: #ffffff;
    --text: #1f2430;
    --muted: #6b7280;
    --line: #e6e9f0;
    --primary: #3b6cf6;
    --primary-dark: #2b55d0;
    --primary-soft: #eef3ff;
    --ok: #0f9d58;
    --ok-soft: #e9f8f0;
    --warn: #b45309;
    --warn-soft: #fff7e6;
    --err: #d93025;
    --err-soft: #fdecea;
    --radius: 16px;
    --shadow: 0 6px 24px rgba(28, 45, 90, .08);
    --shadow-sm: 0 2px 8px rgba(28, 45, 90, .05);
}

* { box-sizing: border-box; }

body {
    margin: 0;
    padding: 0 0 48px;
    background: var(--bg);
    color: var(--text);
    font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", "Microsoft YaHei",
                 "PingFang SC", "Hiragino Sans GB", "Helvetica Neue", Arial, sans-serif;
    font-size: 15px;
    line-height: 1.6;
    -webkit-font-smoothing: antialiased;
}

a { color: var(--primary); text-decoration: none; }
a:hover { text-decoration: underline; }

.wrap { max-width: 960px; margin: 0 auto; padding: 0 18px; }
.wrap-wide { max-width: 1240px; margin: 0 auto; padding: 0 18px; }

/* ---------- 顶部标题 ---------- */
.hero {
    background: linear-gradient(135deg, #3b6cf6 0%, #6d5cf6 55%, #8b5cf6 100%);
    color: #fff;
    padding: 40px 0 76px;
    position: relative;
    overflow: hidden;
}
.hero::after {
    content: "";
    position: absolute;
    right: -80px; top: -80px;
    width: 320px; height: 320px;
    background: rgba(255, 255, 255, .12);
    border-radius: 50%;
}
.hero::before {
    content: "";
    position: absolute;
    right: 130px; bottom: -140px;
    width: 240px; height: 240px;
    background: rgba(255, 255, 255, .08);
    border-radius: 50%;
}
.hero h1 { margin: 0 0 8px; font-size: 28px; letter-spacing: .5px; }
.hero p { margin: 0; opacity: .92; font-size: 14.5px; }
.hero .badge {
    display: inline-block;
    background: rgba(255, 255, 255, .2);
    border: 1px solid rgba(255, 255, 255, .35);
    padding: 3px 12px;
    border-radius: 999px;
    font-size: 12.5px;
    margin-bottom: 14px;
}
.hero-inner { position: relative; z-index: 1; }

/* ---------- 卡片 ---------- */
.card {
    background: var(--card);
    border-radius: var(--radius);
    box-shadow: var(--shadow);
    padding: 26px 28px;
    margin-top: -50px;
    position: relative;
}
.card + .card { margin-top: 20px; }
.card-plain { margin-top: 20px; }
.card h2 {
    margin: 0 0 4px;
    font-size: 18px;
    display: flex;
    align-items: center;
    gap: 9px;
}
.card h2 .num {
    width: 24px; height: 24px;
    background: var(--primary-soft);
    color: var(--primary);
    border-radius: 8px;
    display: inline-flex;
    align-items: center;
    justify-content: center;
    font-size: 13px;
    font-weight: 700;
    flex: none;
}
.card .sub { color: var(--muted); font-size: 13.5px; margin: 0 0 20px; }

/* ---------- 表单 ---------- */
.field { margin-bottom: 18px; }
.field label {
    display: block;
    font-size: 13.5px;
    font-weight: 600;
    margin-bottom: 7px;
}
.field label .req { color: var(--err); margin-left: 3px; }
.field .hint { color: var(--muted); font-size: 12.5px; margin-top: 6px; }

input[type=text], input[type=password], input[type=search], select {
    width: 100%;
    padding: 11px 14px;
    border: 1.5px solid var(--line);
    border-radius: 10px;
    font-size: 15px;
    font-family: inherit;
    color: var(--text);
    background: #fff;
    transition: border-color .15s, box-shadow .15s;
}
input[type=text]:focus, input[type=password]:focus, input[type=search]:focus {
    outline: none;
    border-color: var(--primary);
    box-shadow: 0 0 0 3.5px rgba(59, 108, 246, .13);
}
.grid2 { display: grid; grid-template-columns: 1fr 1fr; gap: 16px; }
@media (max-width: 640px) { .grid2 { grid-template-columns: 1fr; } }

/* ---------- 按钮 ---------- */
.btn {
    display: inline-flex;
    align-items: center;
    justify-content: center;
    gap: 7px;
    padding: 11px 22px;
    border-radius: 10px;
    border: 1.5px solid transparent;
    font-size: 15px;
    font-family: inherit;
    font-weight: 600;
    cursor: pointer;
    text-decoration: none;
    transition: background .15s, border-color .15s, transform .06s;
}
.btn:hover { text-decoration: none; }
.btn:active { transform: translateY(1px); }
.btn-primary { background: var(--primary); color: #fff; }
.btn-primary:hover { background: var(--primary-dark); }
.btn-ghost { background: #fff; border-color: var(--line); color: var(--text); }
.btn-ghost:hover { border-color: #c9d2e5; background: #fafbff; }
.btn-danger { background: #fff; border-color: #f3c4bf; color: var(--err); }
.btn-danger:hover { background: var(--err-soft); }
.btn-sm { padding: 6px 12px; font-size: 13px; border-radius: 8px; }
.btn[disabled] { opacity: .55; cursor: not-allowed; }
.btn-row { display: flex; gap: 12px; align-items: center; flex-wrap: wrap; margin-top: 4px; }

/* ---------- 拖拽上传区 ---------- */
.dropzone {
    border: 2px dashed #ccd6ec;
    border-radius: 14px;
    background: #fafbff;
    padding: 30px 20px;
    text-align: center;
    cursor: pointer;
    transition: border-color .16s, background .16s;
}
.dropzone:hover { border-color: var(--primary); background: var(--primary-soft); }
.dropzone.drag { border-color: var(--primary); background: var(--primary-soft); }
.dropzone .ico { font-size: 34px; line-height: 1; margin-bottom: 10px; }
.dropzone .t1 { font-weight: 600; margin-bottom: 4px; }
.dropzone .t2 { color: var(--muted); font-size: 13px; }
.dropzone input[type=file] { display: none; }

.filelist { margin-top: 14px; display: flex; flex-direction: column; gap: 8px; }
.fileitem {
    display: flex;
    align-items: center;
    gap: 10px;
    background: #fff;
    border: 1px solid var(--line);
    border-radius: 10px;
    padding: 9px 12px;
    font-size: 13.5px;
}
.fileitem .fname { flex: 1; word-break: break-all; }
.fileitem .fsize { color: var(--muted); font-size: 12.5px; white-space: nowrap; }
.fileitem .rm {
    border: none; background: none; color: var(--muted);
    cursor: pointer; font-size: 16px; line-height: 1; padding: 2px 4px;
}
.fileitem .rm:hover { color: var(--err); }
.fileitem.bad { border-color: #f3c4bf; background: var(--err-soft); }
.fileitem.bad .fname { color: var(--err); }

/* ---------- 提示条 ---------- */
.alert {
    border-radius: 12px;
    padding: 13px 16px;
    font-size: 14px;
    margin-bottom: 16px;
    border: 1px solid transparent;
}
.alert ul { margin: 6px 0 0; padding-left: 20px; }
.alert-ok { background: var(--ok-soft); border-color: #bfe6d1; color: #0b6b3c; }
.alert-err { background: var(--err-soft); border-color: #f3c4bf; color: #9c1f16; }
.alert-warn { background: var(--warn-soft); border-color: #f2d9a4; color: var(--warn); }
.alert-info { background: var(--primary-soft); border-color: #cfdcff; color: #2b4bb5; }
.alert strong { font-weight: 700; }

/* ---------- 徽标 / 标签 ---------- */
.tag {
    display: inline-block;
    padding: 2px 9px;
    border-radius: 999px;
    font-size: 12px;
    background: var(--primary-soft);
    color: var(--primary);
    white-space: nowrap;
}
.tag-ok { background: var(--ok-soft); color: var(--ok); }
.tag-gray { background: #f1f3f7; color: var(--muted); }

/* ---------- 表格 ---------- */
.table-wrap { overflow-x: auto; border: 1px solid var(--line); border-radius: 12px; }
table.data {
    width: 100%;
    border-collapse: collapse;
    font-size: 13.5px;
    background: #fff;
}
table.data th, table.data td {
    padding: 11px 13px;
    text-align: left;
    border-bottom: 1px solid var(--line);
    vertical-align: middle;
}
table.data th {
    background: #f8faff;
    font-weight: 600;
    color: #48506b;
    font-size: 12.5px;
    white-space: nowrap;
}
table.data tr:last-child td { border-bottom: none; }
table.data tr:hover td { background: #fbfcff; }
table.data td.nowrap { white-space: nowrap; color: var(--muted); font-size: 12.5px; }

/* ---------- 统计小卡 ---------- */
.stats { display: grid; grid-template-columns: repeat(4, 1fr); gap: 14px; margin-bottom: 20px; }
@media (max-width: 700px) { .stats { grid-template-columns: repeat(2, 1fr); } }
.stat {
    background: #fff;
    border: 1px solid var(--line);
    border-radius: 12px;
    padding: 14px 16px;
}
.stat .k { color: var(--muted); font-size: 12.5px; margin-bottom: 4px; }
.stat .v { font-size: 22px; font-weight: 700; letter-spacing: .3px; }
.stat .v small { font-size: 13px; font-weight: 500; color: var(--muted); }

/* ---------- 学生分组折叠 ---------- */
details.stu {
    border: 1px solid var(--line);
    border-radius: 12px;
    margin-bottom: 10px;
    background: #fff;
    overflow: hidden;
}
details.stu > summary {
    cursor: pointer;
    padding: 12px 16px;
    display: flex;
    align-items: center;
    gap: 12px;
    list-style: none;
    font-size: 14px;
}
details.stu > summary::-webkit-details-marker { display: none; }
details.stu > summary::before {
    content: "▸";
    color: var(--muted);
    font-size: 12px;
    transition: transform .15s;
}
details.stu[open] > summary::before { transform: rotate(90deg); }
details.stu > summary:hover { background: #fafbff; }
details.stu .sname { font-weight: 600; }
details.stu .smeta { color: var(--muted); font-size: 12.5px; margin-left: auto; }
details.stu .body { padding: 0 16px 14px 30px; }

/* ---------- 页脚 ---------- */
.foot {
    text-align: center;
    color: #9aa3b8;
    font-size: 12.5px;
    margin-top: 26px;
}
.foot code {
    background: #eef1f8;
    padding: 1px 6px;
    border-radius: 5px;
    font-size: 12px;
}

/* ---------- 教师端工具栏 ---------- */
.toolbar {
    display: flex;
    gap: 12px;
    align-items: center;
    flex-wrap: wrap;
    margin-bottom: 18px;
}
.toolbar .grow { flex: 1; min-width: 180px; }
.toolbar form { display: flex; gap: 10px; align-items: center; flex: 1; min-width: 220px; }

/* ---------- 打印 ---------- */
@media print {
    .hero, .no-print { display: none !important; }
    .card { margin-top: 0; box-shadow: none; border: 1px solid var(--line); }
    body { background: #fff; }
}