:root {
    --bg: #0f172a;
    --card: #1e293b;
    --text: #f1f5f9;
    --muted: #94a3b8;
    --border: #475569;
    --input: #0f172a;
    --green: #22c55e;
    --blue: #3b82f6;
}

/* 象牙白亮色主題 */
body.light {
    --bg: #f5f2e9;
    --card: #fffdf5;
    --text: #2b2a26;
    --muted: #8a8578;
    --border: #e0dccf;
    --input: #fdfbf3;
}

* { box-sizing: border-box; }

body {
    margin: 0;
    font-family: -apple-system, "Segoe UI", "Microsoft JhengHei", Arial, sans-serif;
    background: var(--bg);
    color: var(--text);
    min-height: 100vh;
    display: flex;
    flex-direction: column;
    justify-content: center;
    align-items: center;
    padding: 40px 0;
    transition: background .3s, color .3s;
}

.topbar {
    position: fixed;
    top: 16px;
    right: 16px;
    display: flex;
    gap: 8px;
    z-index: 10;
}

.icon-btn {
    background: var(--card);
    color: var(--text);
    border: 1px solid var(--border);
    padding: 8px 12px;
    border-radius: 8px;
    cursor: pointer;
    font-size: 14px;
}
.icon-btn:hover { opacity: .85; }

.container { width: 90%; max-width: 600px; }

h1 { text-align: center; margin-bottom: 8px; }

.subtitle {
    text-align: center;
    color: var(--muted);
    margin-bottom: 30px;
}

.card {
    background: var(--card);
    padding: 30px;
    border-radius: 16px;
    box-shadow: 0 10px 30px rgba(0,0,0,.15);
}

.drop-zone {
    border: 2px dashed var(--border);
    border-radius: 12px;
    padding: 30px;
    text-align: center;
    color: var(--muted);
    cursor: pointer;
    margin-bottom: 15px;
    transition: all .2s;
    word-break: break-all;
}
.drop-zone.dragover { border-color: var(--green); color: var(--green); }
.drop-zone.has-file { border-color: var(--blue); color: var(--blue); }

.pw-row { display: flex; gap: 8px; margin-bottom: 10px; }

.pw-row input {
    flex: 1;
    padding: 12px;
    border-radius: 8px;
    border: 1px solid var(--border);
    background: var(--input);
    color: var(--text);
    font-size: 15px;
}

.mini-btn {
    background: var(--card);
    color: var(--text);
    border: 1px solid var(--border);
    border-radius: 8px;
    padding: 0 12px;
    cursor: pointer;
    white-space: nowrap;
    font-size: 14px;
}
.mini-btn:hover { opacity: .85; }

.pw-strength {
    height: 6px;
    border-radius: 3px;
    margin-bottom: 15px;
    background: var(--border);
    overflow: hidden;
    transition: all .3s;
}
.pw-strength span {
    display: block;
    height: 100%;
    width: 0%;
    transition: width .3s, background .3s;
}

.buttons { display: flex; gap: 10px; }

.buttons button {
    flex: 1;
    border: none;
    padding: 12px;
    cursor: pointer;
    border-radius: 8px;
    font-size: 16px;
    color: white;
    transition: opacity .2s;
}
#encryptBtn { background: var(--green); }
#decryptBtn { background: var(--blue); }
.buttons button:hover:not(:disabled) { opacity: .9; }
.buttons button:disabled { opacity: .5; cursor: not-allowed; }

.progress-wrap {
    display: none;
    margin-top: 20px;
    height: 8px;
    background: var(--border);
    border-radius: 4px;
    overflow: hidden;
}
.progress-bar {
    height: 100%;
    width: 0%;
    background: var(--green);
    transition: width .1s linear;
}

#status {
    margin-top: 16px;
    text-align: center;
    min-height: 20px;
}

.features {
    margin-top: 20px;
    display: grid;
    grid-template-columns: 1fr 1fr;
    gap: 10px;
    color: var(--muted);
    font-size: 14px;
}

/* ========= 科普說明區 ========= */
.info-block {
    margin-top: 24px;
    background: var(--card);
    border: 1px solid var(--border);
    border-radius: 16px;
    overflow: hidden;
}

.info-header {
    width: 100%;
    background: transparent;
    color: var(--text);
    border: none;
    padding: 18px 20px;
    font-size: 16px;
    font-weight: 600;
    cursor: pointer;
    display: flex;
    justify-content: space-between;
    align-items: center;
}
.info-header:hover { opacity: .85; }

.arrow { transition: transform .3s; color: var(--muted); }
.arrow.open { transform: rotate(180deg); }

.info-body {
    display: none;
    padding: 0 20px 20px;
    color: var(--text);
    line-height: 1.7;
    font-size: 15px;
}
.info-body.open { display: block; }

.info-lead {
    background: rgba(34,197,94,.12);
    border-left: 3px solid var(--green);
    padding: 12px 14px;
    border-radius: 8px;
    color: var(--text);
}

.info-body h3 {
    margin: 22px 0 8px;
    font-size: 16px;
}

.spec-table {
    width: 100%;
    border-collapse: collapse;
    font-size: 14px;
}
.spec-table td {
    padding: 8px 10px;
    border-bottom: 1px solid var(--border);
}
.spec-table td:first-child { color: var(--muted); width: 42%; }

.limit-list {
    margin: 8px 0 0;
    padding-left: 20px;
    color: var(--text);
}
.limit-list li { margin-bottom: 8px; }

/* =========================
   Mobile Responsive
   ========================= */

@media (max-width: 768px) {

    body {
        padding: 80px 0 40px;
    }

    .container {
        width: 92%;
        max-width: 100%;
    }

    h1 {
        font-size: 2rem;
        line-height: 1.3;
        margin-bottom: 10px;
    }

    .subtitle {
        font-size: 1rem;
        margin-bottom: 20px;
    }

    .topbar {
        top: 12px;
        right: 12px;
        gap: 8px;
    }

    .icon-btn {
        padding: 8px 12px;
        font-size: 14px;
        min-width: 52px;
    }

    .card {
        padding: 20px;
    }

    .drop-zone {
        padding: 24px 16px;
        font-size: 1rem;
    }

    /* 密碼欄位換行 */

    .pw-row {
        flex-wrap: wrap;
    }

    .pw-row input {
        flex: 0 0 100%;
        width: 100%;
    }

    .mini-btn {
        flex: 1;
        height: 48px;
    }

    /* 強度條 */

    .pw-strength {
        margin-top: 8px;
    }

    /* 按鈕改上下排列 */

    .buttons {
        flex-direction: column;
    }

    .buttons button {
        width: 100%;
        min-height: 52px;
    }

    /* 科普區 */

    .info-header {
        font-size: 15px;
        padding: 16px;
    }

    .info-body {
        font-size: 14px;
        padding: 0 16px 16px;
    }

    .spec-table {
        display: block;
        overflow-x: auto;
    }
}