/* -----------------------------------------------------------
   Design Specification: "THE MINIMAL MANUAL"
   Focus: Pure White, Deep Space, Dynamic Typography
   ----------------------------------------------------------- */

:root {
    --bg-base: #f9f7f5; /* 上品なグレージュ */
    --bg-sub: #fcfcfc;
    --main-color: #607d8b; /* ブルーグレー：統計・信頼 */
    --accent-color: #9c27b0; /* 紫：運気・未来 */
    --text-base: #2c3e50;
    --card-bg: rgba(255, 255, 255, 0.85);
    --white: #ffffff;

    --text-primary: #1a1a1a;    /* 強い信頼感のある黒 [4] */
    --text-secondary: #888888;  /* 空間に溶け込むグレー [5] */
    --accent: #000000;          /* 2026年は黒が最大のアクセント [1] */
    --border: #eeeeee;
    --font-logic: 'Montserrat', sans-serif;
    --font-serif: 'Noto Serif JP', serif;

}

body, html {
    margin: 0; padding: 0; min-height: 100vh;
    display: flex; justify-content: center; align-items: center;
    background-color: var(--bg-base);
    font-family: 'Montserrat', 'Noto Serif JP', serif;
    color: var(--text-base);
    overflow-x: hidden;
}

/* 質感の演出：多色グラデーションと紙のテクスチャ [3] */
.background-overlay {
    position: fixed; top: 0; left: 0; width: 100%; height: 100%;
    background: radial-gradient(circle at 10% 20%, rgba(156, 39, 176, 0.03) 0%, transparent 40%),
                radial-gradient(circle at 90% 80%, rgba(96, 125, 139, 0.05) 0%, transparent 40%);
    z-index: -2;
}

body::after {
    content: ""; position: fixed; top: 0; left: 0; width: 100%; height: 100%;
    background-image: url("https://www.transparenttextures.com/patterns/natural-paper.png");
    opacity: 0.4; pointer-events: none; z-index: -1;
}

/* 共通カードデザイン：ジェネレーティブUIを意識した透明感 [5] */
.auth-card {
    background: var(--card-bg);
    backdrop-filter: blur(12px);
    padding: 3rem 2rem;
    border-radius: 24px;
    box-shadow: 0 15px 35px rgba(0,0,0,0.03);
    width: 100%; max-width: 400px;
    text-align: center; box-sizing: border-box; margin: 20px;
}

.brand-name {
    font-size: 0.8rem; letter-spacing: 0.5rem; font-weight: 200;
    color: var(--main-color); margin-bottom: 0.5rem; text-transform: uppercase;
}

.title {
    font-family: 'Noto Serif JP', serif;
    font-size: 1.5rem; font-weight: 700; margin-bottom: 2rem;
}

/* フォーム要素：アクセシビリティ（使いやすさ）重視 [1, 2] */
.form-group { text-align: left; margin-bottom: 1.2rem; }
label { display: block; font-size: 0.85rem; color: var(--main-color); margin-bottom: 0.4rem; }
input {
    width: 100%; padding: 14px; border: 1px solid #e0dcd9;
    border-radius: 10px; font-size: 1rem; box-sizing: border-box;
    background: rgba(255, 255, 255, 0.6); transition: 0.3s;
}
input:focus { outline: none; border-color: var(--accent-color); box-shadow: 0 0 0 4px rgba(156, 39, 176, 0.1); }

/* ボタン：行動喚起（CTA）の配色戦略 [6, 7] */
.btn {
    width: 100%; padding: 16px; background: var(--main-color);
    color: var(--white); border: none; border-radius: 10px;
    font-size: 1rem; font-weight: 600; cursor: pointer;
    transition: 0.4s cubic-bezier(0.25, 0.8, 0.25, 1);
    margin-top: 1rem; letter-spacing: 0.1rem;
}
.btn:hover { background: var(--accent-color); transform: translateY(-2px); box-shadow: 0 8px 20px rgba(156, 39, 176, 0.2); }

.links { margin-top: 1.5rem; font-size: 0.8rem; }
.links a { color: var(--main-color); text-decoration: none; opacity: 0.7; margin: 0 5px; }
.links a:hover { opacity: 1; text-decoration: underline; }

/* モバイル最適化 [2] */
@media (max-width: 480px) {
    .auth-card { padding: 2.5rem 1.5rem; }
    .title { font-size: 1.3rem; }
}