/* =============================================
   Variables
   ============================================= */
:root,
[data-theme="light"] {
    --bg: #ffffff;
    --bg-secondary: #f5f6f8;
    --text: #24292e;
    --text-secondary: #57606a;
    --border: #d0d7de;
    --accent: #0969da;
    --tab-bg: #f5f6f8;
    --tab-active-bg: #ffffff;
    --tab-active-border: #0969da;
    --table-header-bg: #f6f8fa;
    --table-stripe: #f6f8fa;
    --blockquote-bg: #f6f8fa;
    --code-bg: #eff1f3;
    --topbar-bg: #ffffff;
    --topbar-border: #d0d7de;
}

[data-theme="dark"] {
    --bg: #0d1117;
    --bg-secondary: #161b22;
    --text: #e6edf3;
    --text-secondary: #8b949e;
    --border: #30363d;
    --accent: #58a6ff;
    --tab-bg: #161b22;
    --tab-active-bg: #0d1117;
    --tab-active-border: #58a6ff;
    --table-header-bg: #161b22;
    --table-stripe: #161b22;
    --blockquote-bg: #161b22;
    --code-bg: #161b22;
    --topbar-bg: #161b22;
    --topbar-border: #30363d;
}

/* =============================================
   Reset & Base
   ============================================= */
*, *::before, *::after {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
}

html {
    -webkit-text-size-adjust: 100%;
}

body {
    font-family: 'Inter', -apple-system, BlinkMacSystemFont, "Segoe UI", Helvetica, Arial, sans-serif;
    background: var(--bg);
    color: var(--text);
    line-height: 1.6;
    -webkit-font-smoothing: antialiased;
}

/* =============================================
   Top Bar
   ============================================= */
.topbar {
    position: sticky;
    top: 0;
    z-index: 50;
    background: var(--topbar-bg);
    border-bottom: 1px solid var(--topbar-border);
}

.topbar-inner {
    max-width: 860px;
    margin: 0 auto;
    padding: 12px 20px;
    display: flex;
    align-items: center;
    justify-content: space-between;
}

.topbar-title {
    font-size: 15px;
    font-weight: 600;
    color: var(--text);
}

.theme-btn {
    background: none;
    border: 1px solid var(--border);
    color: var(--text-secondary);
    width: 34px;
    height: 34px;
    border-radius: 6px;
    display: flex;
    align-items: center;
    justify-content: center;
    cursor: pointer;
}

.theme-btn:hover {
    color: var(--text);
    border-color: var(--text-secondary);
}

[data-theme="light"] .icon-sun { display: none; }
[data-theme="light"] .icon-moon { display: block; }
[data-theme="dark"] .icon-sun { display: block; }
[data-theme="dark"] .icon-moon { display: none; }

/* =============================================
   Unit Tabs (horizontal scrollable)
   ============================================= */
.unit-tabs {
    position: sticky;
    top: 59px; /* height of topbar */
    z-index: 40;
    background: var(--topbar-bg);
    border-bottom: 1px solid var(--topbar-border);
    display: flex;
    overflow-x: auto;
    -webkit-overflow-scrolling: touch;
    scrollbar-width: none;
}

.unit-tabs::-webkit-scrollbar {
    display: none;
}

.unit-tab {
    flex: 0 0 auto;
    padding: 10px 20px;
    font-size: 14px;
    font-weight: 500;
    font-family: inherit;
    color: var(--text-secondary);
    background: none;
    border: none;
    border-bottom: 2px solid transparent;
    cursor: pointer;
    white-space: nowrap;
    transition: color 0.15s, border-color 0.15s;
}

.unit-tab:hover {
    color: var(--text);
}

.unit-tab.active {
    color: var(--accent);
    border-bottom-color: var(--accent);
}

/* =============================================
   Type Tabs (Full Answers / Quick Revision)
   ============================================= */
.type-tabs {
    max-width: 860px;
    margin: 0 auto;
    padding: 16px 20px 0;
    display: flex;
    gap: 6px;
}

.type-tab {
    padding: 7px 16px;
    font-size: 13px;
    font-weight: 500;
    font-family: inherit;
    color: var(--text-secondary);
    background: var(--tab-bg);
    border: 1px solid var(--border);
    border-radius: 6px;
    cursor: pointer;
    transition: all 0.15s;
}

.type-tab:hover {
    color: var(--text);
}

.type-tab.active {
    background: var(--accent);
    color: #ffffff;
    border-color: var(--accent);
}

/* =============================================
   Main Content
   ============================================= */
.content {
    max-width: 860px;
    margin: 0 auto;
    padding: 20px 20px 60px;
}

.content-inner {
    animation: fadeIn 0.25s ease;
}

@keyframes fadeIn {
    from { opacity: 0; }
    to { opacity: 1; }
}

.placeholder-text {
    text-align: center;
    padding: 40px 0;
    color: var(--text-secondary);
    font-size: 14px;
}

/* =============================================
   Markdown Rendered Styles
   ============================================= */
.content-inner h1 {
    font-size: 24px;
    font-weight: 700;
    margin: 0 0 12px;
    padding-bottom: 8px;
    border-bottom: 1px solid var(--border);
    line-height: 1.3;
}

.content-inner h2 {
    font-size: 20px;
    font-weight: 600;
    margin: 28px 0 10px;
    padding-bottom: 6px;
    border-bottom: 1px solid var(--border);
    line-height: 1.3;
}

.content-inner h3 {
    font-size: 16px;
    font-weight: 600;
    margin: 22px 0 8px;
    line-height: 1.4;
}

.content-inner h4 {
    font-size: 14px;
    font-weight: 600;
    margin: 18px 0 6px;
}

.content-inner p {
    margin-bottom: 12px;
    color: var(--text-secondary);
    font-size: 14px;
    line-height: 1.7;
}

.content-inner ul,
.content-inner ol {
    margin-bottom: 12px;
    padding-left: 22px;
    color: var(--text-secondary);
    font-size: 14px;
}

.content-inner li {
    margin-bottom: 4px;
    line-height: 1.6;
}

.content-inner li > ul,
.content-inner li > ol {
    margin-top: 4px;
    margin-bottom: 4px;
}

.content-inner strong {
    color: var(--text);
    font-weight: 600;
}

.content-inner em {
    font-style: italic;
}

.content-inner a {
    color: var(--accent);
    text-decoration: none;
}

.content-inner a:hover {
    text-decoration: underline;
}

/* Blockquote */
.content-inner blockquote {
    margin: 12px 0;
    padding: 10px 16px;
    border-left: 3px solid var(--accent);
    background: var(--blockquote-bg);
    color: var(--text-secondary);
    font-size: 14px;
    border-radius: 0 4px 4px 0;
}

.content-inner blockquote p {
    margin-bottom: 6px;
}

.content-inner blockquote p:last-child {
    margin-bottom: 0;
}

/* Horizontal Rule */
.content-inner hr {
    border: none;
    height: 1px;
    background: var(--border);
    margin: 24px 0;
}

/* Tables */
.table-wrapper {
    overflow-x: auto;
    margin: 14px 0;
    border: 1px solid var(--border);
    border-radius: 6px;
}

.content-inner table {
    width: 100%;
    border-collapse: collapse;
    font-size: 13px;
    white-space: normal;
}

.content-inner th,
.content-inner td {
    padding: 8px 12px;
    text-align: left;
    border-bottom: 1px solid var(--border);
    vertical-align: top;
}

.content-inner th {
    background: var(--table-header-bg);
    font-weight: 600;
    color: var(--text);
    white-space: nowrap;
}

.content-inner td {
    color: var(--text-secondary);
}

.content-inner tr:last-child td {
    border-bottom: none;
}

.content-inner tr:nth-child(even) td {
    background: var(--table-stripe);
}

/* Code */
.content-inner code {
    font-family: ui-monospace, SFMono-Regular, "SF Mono", Menlo, Consolas, monospace;
    font-size: 12px;
    background: var(--code-bg);
    padding: 2px 6px;
    border-radius: 4px;
    color: var(--text);
}

.content-inner pre {
    margin: 12px 0;
    padding: 14px;
    background: var(--code-bg);
    border: 1px solid var(--border);
    border-radius: 6px;
    overflow-x: auto;
    font-size: 13px;
    line-height: 1.5;
}

.content-inner pre code {
    background: none;
    padding: 0;
    font-size: inherit;
}

/* Loading */
.loader-wrap {
    display: flex;
    justify-content: center;
    padding: 50px 0;
}

.loader {
    width: 28px;
    height: 28px;
    border: 3px solid var(--border);
    border-top-color: var(--accent);
    border-radius: 50%;
    animation: spin 0.7s linear infinite;
}

@keyframes spin {
    to { transform: rotate(360deg); }
}

/* =============================================
   Responsive — small tweaks for desktop
   ============================================= */
@media (min-width: 768px) {
    .unit-tabs {
        justify-content: center;
    }

    .unit-tab {
        padding: 10px 28px;
    }

    .type-tabs {
        padding-top: 20px;
    }

    .content {
        padding: 24px 20px 80px;
    }

    .content-inner h1 {
        font-size: 28px;
    }

    .content-inner h2 {
        font-size: 22px;
    }

    .content-inner h3 {
        font-size: 17px;
    }

    .content-inner p,
    .content-inner ul,
    .content-inner ol,
    .content-inner blockquote {
        font-size: 15px;
    }

    .content-inner table {
        font-size: 14px;
    }
}