:root {
    --brand:       #6644CC;
    --brand-light: #8B5CF6;
    --bg:          #F5F5F7;
    --surface:     #FFFFFF;
    --border:      #D2D2D7;
    --text:        #333333;
    --text-muted:  #999999;
    --danger:      #F85149;
    --success:     #3FB950;
    --radius:      14px;
    --radius-sm:   8px;
}
* { margin: 0; padding: 0; box-sizing: border-box; }
body {
    font-family: 'PingFang SC', 'Microsoft YaHei', -apple-system, sans-serif;
    background: var(--bg);
    color: var(--text);
    font-size: 14px;
    line-height: 1.6;
    -webkit-font-smoothing: antialiased;
    min-height: 100vh;
    display: flex;
    align-items: center;
    justify-content: center;
    padding: 20px;
}
.login-card {
    width: 100%;
    max-width: 380px;
    background: var(--surface);
    border-radius: var(--radius);
    box-shadow: 0 4px 24px rgba(0,0,0,.08);
    overflow: hidden;
}
.login-header {
    background: linear-gradient(135deg, #6644CC 0%, #8B5CF6 40%, #A78BFA 70%, #7B42C8 100%);
    padding: 28px 32px 28px;
    text-align: center;
}
.login-logo {
    display: inline-flex;
    align-items: center;
    gap: 14px;
}
.logo-img {
    height: 22px;
    width: auto;
    filter: brightness(0) invert(1);
}
.login-body {
    padding: 28px 32px 32px;
}
.form-group {
    margin-bottom: 18px;
}
.form-label {
    display: block;
    font-size: 13px;
    font-weight: 600;
    color: var(--text);
    margin-bottom: 8px;
}
.form-input {
    width: 100%;
    padding: 12px 14px;
    border: 1.5px solid var(--border);
    border-radius: var(--radius-sm);
    font-size: 15px;
    font-family: inherit;
    color: var(--text);
    background: var(--surface);
    transition: border-color .2s, box-shadow .2s;
    outline: none;
}
.form-input:focus {
    border-color: var(--brand);
    box-shadow: 0 0 0 3px rgba(102,68,204,.12);
}
.form-input.error {
    border-color: var(--danger);
    box-shadow: 0 0 0 3px rgba(248,81,73,.1);
}
.btn-login {
    width: 100%;
    padding: 13px;
    border: none;
    border-radius: var(--radius-sm);
    background: var(--brand);
    color: #FFFFFF;
    font-size: 15px;
    font-weight: 700;
    font-family: inherit;
    cursor: pointer;
    transition: background .2s, transform .1s;
    letter-spacing: .5px;
}
.btn-login:hover { background: var(--brand-light); }
.btn-login:active { transform: scale(.98); }
.btn-login:disabled {
    background: var(--border);
    cursor: not-allowed;
}
.error-msg {
    color: var(--danger);
    font-size: 13px;
    font-weight: 500;
    margin-top: 10px;
    text-align: center;
    min-height: 20px;
}
.login-footer {
    text-align: center;
    font-size: 11px;
    color: var(--text-muted);
    margin-top: 20px;
    font-weight: 500;
}
@media (max-width: 640px) {
    body { padding: 12px; }
    .login-header { padding: 22px 18px 22px; }
    .logo-img { height: 18px; }
    .login-body { padding: 22px 18px 26px; }
}