/* 登录页面自定义美化样式（无Bootstrap） */
body {
    background: linear-gradient(135deg, #e0e7ff 0%, #fff 100%);
    min-height: 100vh;
    margin: 0;
    font-family: 'PingFang SC', 'Microsoft YaHei', Arial, sans-serif;
}
.container {
    background: #fff;
    border-radius: 18px;
    box-shadow: 0 6px 32px rgba(60, 72, 88, 0.15);
    padding: 36px 28px 28px 28px;
    margin: 60px auto 0 auto;
    max-width: 400px;
}
.alert {
    display: flex;
    justify-content: center;
    align-items: center;
    text-align: center;
    font-weight: 600;
    color: #a94442;
    background: #f8d7da;
    border: 1px solid #f5c6cb;
    border-radius: 10px;
    width: 100%;
    min-height: 48px;
    font-size: 1.15rem;
    margin-bottom: 18px;
    box-sizing: border-box;
}
h3.text-center {
    font-weight: 700;
    color: #4f8cff;
    letter-spacing: 2px;
    text-align: center;
    margin-bottom: 24px;
}
.form-group {
    margin-bottom: 22px;
    width: 100%;
}
.form-group label {
    font-weight: 500;
    color: #333;
    display: block;
    margin-bottom: 7px;
}
.form-control {
    width: 100%;
    border-radius: 8px;
    border: 1px solid #cfd8dc;
    box-shadow: none;
    padding: 12px 14px;
    font-size: 1rem;
    transition: border-color 0.2s;
    outline: none;
    box-sizing: border-box;
}
.form-control:focus {
    border-color: #4f8cff;
    box-shadow: 0 0 0 2px #e3f0ff;
}
.btn-success {
    width: 100%;
    background: #4f8cff;
    border: none;
    border-radius: 8px;
    font-weight: 600;
    font-size: 1.1rem;
    color: #fff;
    padding: 12px 0;
    box-shadow: 0 2px 8px rgba(79,140,255,0.08);
    transition: background 0.2s, box-shadow 0.2s;
    cursor: pointer;
    margin-top: 8px;
}
.btn-success:hover {
    background: #2566d6;
    box-shadow: 0 4px 16px rgba(56,207,166,0.12);
}
.text-center {
    text-align: center;
    margin-top: 22px;
}
.text-center a {
    color: #4f8cff;
    text-decoration: none;
    transition: color 0.2s;
    font-size: 1rem;
}
.text-center a:hover {
    color: #38cfa6;
    text-decoration: underline;
}
.invalid-feedback.d-block {
    color: #e74c3c;
    font-size: 0.97rem;
    margin-top: 2px;
    margin-bottom: 2px;
    font-weight: 500;
}
@media (max-width: 500px) {
    .container {
        padding: 18px 6px 18px 6px;
        margin-top: 20px !important;
    }
    h3.text-center {
        font-size: 1.3rem;
    }
}