:root {
    --page-bg: #f5f5f5;
    --surface: #ffffff;
    --control-bg: #ffffff;
    --line: #dddddd;
    --text: #333333;
    --heading: #555555;
    --muted: #777777;
    --brand: #28a745;
    --brand-contrast: #ffffff;
    --danger: #dc3545;
    --shadow: 0 2px 12px rgba(0, 0, 0, .15);
    --header-control-border: rgba(255, 255, 255, .55);
    --header-control-hover-bg: rgba(255, 255, 255, .15);
    --header-control-hover-border: rgba(255, 255, 255, .78);
  }

  html[data-theme="dark"] {
    --page-bg: #101216;
    --surface: #171a21;
    --control-bg: #1e2330;
    --line: #303746;
    --text: #f4f7fb;
    --heading: #d6dde8;
    --muted: #a7b0bf;
    --brand: #35c765;
    --brand-contrast: #ffffff;
    --danger: #f87171;
    --shadow: 0 2px 16px rgba(0, 0, 0, .35);
    --header-control-border: rgba(255, 255, 255, .5);
    --header-control-hover-bg: rgba(255, 255, 255, .15);
    --header-control-hover-border: rgba(255, 255, 255, .75);
  }

  * { box-sizing: border-box; margin: 0; padding: 0; }
  body {
    font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, sans-serif;
    background: var(--page-bg); color: var(--text); font-size: 14px;
    display: flex; flex-direction: column; min-height: 100vh;
  }
  header {
    background: var(--brand); color: var(--brand-contrast);
    padding: 14px 20px; font-size: 18px; font-weight: bold; letter-spacing: .5px;
    display: flex; align-items: center; gap: 12px;
  }
  .header-title { flex: 1; min-width: 0; }
  .header-actions { display: inline-flex; align-items: center; gap: 8px; flex-shrink: 0; }
  .pixiv-lang-switcher--login {
    display: inline-flex; align-items: center; font-size: 12px; font-weight: 500;
  }
  .pixiv-lang-switcher--login .pixiv-lang-switcher__select {
    min-height: 28px; padding: 3px 7px;
    border: 1px solid var(--header-control-border); border-radius: 4px;
    background: transparent; color: var(--brand-contrast); cursor: pointer;
    font-size: 12px; font-family: inherit;
  }
  .pixiv-lang-switcher--login .pixiv-lang-switcher__select:hover {
    background: var(--header-control-hover-bg); border-color: var(--header-control-hover-border);
  }
  .pixiv-lang-switcher--login .pixiv-lang-switcher__select option {
    background: var(--surface); color: var(--text);
  }
  .pixiv-theme-toggle--login {
    width: 28px; height: 28px;
    border: 1px solid var(--header-control-border); border-radius: 4px;
    background: transparent; color: var(--brand-contrast); cursor: pointer;
    display: inline-flex; align-items: center; justify-content: center;
    transition: background .2s, border-color .2s;
  }
  .pixiv-theme-toggle--login:hover {
    background: var(--header-control-hover-bg); border-color: var(--header-control-hover-border);
  }
  .pixiv-theme-toggle--login svg {
    width: 15px; height: 15px;
    fill: none; stroke: currentColor; stroke-width: 2;
    stroke-linecap: round; stroke-linejoin: round;
  }
  .center {
    flex: 1; display: flex; align-items: center; justify-content: center;
    padding: 20px;
  }
  .card {
    background: var(--surface); border-radius: 8px;
    box-shadow: var(--shadow);
    padding: 28px; width: 100%; max-width: 360px;
  }
  .card-title {
    font-weight: bold; font-size: 13px; color: var(--heading);
    margin-bottom: 20px; text-transform: uppercase; letter-spacing: .4px;
  }
  .field { margin-bottom: 14px; }
  .field label { display: block; font-size: 12px; color: var(--heading); margin-bottom: 4px; font-weight: bold; }
  .field input[type=text],
  .field input[type=password] {
    width: 100%; padding: 9px 11px;
    border: 1px solid var(--line); border-radius: 5px;
    background: var(--control-bg); color: var(--text);
    font-size: 13px; transition: border-color .15s;
  }
  .field input::placeholder { color: var(--muted); }
  .field input:focus { outline: none; border-color: var(--brand); }
  .remember-row {
    display: flex; align-items: center; gap: 8px;
    margin-bottom: 18px;
  }
  .remember-row input[type=checkbox] { width: 15px; height: 15px; cursor: pointer; accent-color: var(--brand); }
  .remember-row label { font-size: 13px; cursor: pointer; color: var(--heading); }
  #error-msg,
  #invite-error {
    font-size: 12px; color: var(--danger);
    min-height: 18px; margin-bottom: 10px; text-align: center;
  }
  .btn {
    display: block; width: 100%; padding: 10px;
    border: none; border-radius: 5px; cursor: pointer;
    font-size: 14px; font-weight: bold; color: var(--brand-contrast); transition: opacity .15s;
  }
  .btn:hover { opacity: .85; }
  .btn:disabled { opacity: .45; cursor: not-allowed; }
  .btn-green { background: var(--brand); }
  .invite-link-row {
    margin-top: 14px; text-align: center; font-size: 12px;
  }
  .invite-link-row a { color: var(--brand); cursor: pointer; text-decoration: underline; }
  .hidden { display: none; }