* { margin: 0; padding: 0; box-sizing: border-box; }
body {
    font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', sans-serif;
    background: #f5f6fa;
    min-height: 100vh;
    display: flex;
    align-items: center;
    justify-content: center;
}
.login-box {
    background: #fff;
    border-radius: 6px;
    box-shadow: 0 1px 4px rgba(0,0,0,.06);
    width: 340px;
    padding: 36px 32px 30px;
}
.login-box h2 {
    text-align: center;
    font-size: 20px;
    color: #1a1a1a;
    font-weight: 500;
    margin-bottom: 28px;
    letter-spacing: 2px;
}
.form-item {
    margin-bottom: 18px;
}
.form-item input {
    width: 100%;
    padding: 10px 0;
    border: none;
    border-bottom: 1px solid #e8e8e8;
    font-size: 14px;
    color: #333;
    outline: none;
    transition: border-color .2s;
    background: transparent;
}
.form-item input::placeholder { color: #bbb; }
.form-item input:focus { border-bottom-color: #4a6cf7; }
.captcha-row {
    display: flex;
    gap: 10px;
}
.captcha-row input { flex: 1; }
.captcha-row img {
    height: 40px;
    border: 1px solid #e8e8e8;
    border-radius: 4px;
    cursor: pointer;
}
.btn {
    width: 100%;
    padding: 11px;
    background: #4a6cf7;
    color: #fff;
    border: none;
    border-radius: 4px;
    font-size: 15px;
    cursor: pointer;
    margin-top: 6px;
    transition: background .2s;
}
.btn:hover { background: #3b5de7; }
.tip {
    text-align: center;
    color: #e74c3c;
    font-size: 13px;
    margin-top: 14px;
    display: none;
}