.sidebar {
    width: var(--sidebar-width);
    background: var(--glass-bg);
    backdrop-filter: blur(24px) saturate(180%);
    -webkit-backdrop-filter: blur(24px) saturate(180%);
    border-right: 1px solid var(--glass-border);
    display: flex; flex-direction: column;
    padding: 20px 18px;
    z-index: 10; position: relative; overflow: hidden;
}
.sidebar::before {
    content: '';
    position: absolute; inset: 0;
    background: radial-gradient(900px 400px at -10% -20%, var(--accent-faint), transparent 60%);
    pointer-events: none;
}

.sidebar-header { display: flex; justify-content: space-between; align-items: center; margin-bottom: 22px; position: relative; }
.sidebar-header h2 { font-size: 18px; font-weight: 700; letter-spacing: -0.4px; display: flex; align-items: center; gap: 8px; }
.sidebar-header h2 img { border-radius: 6px; }
.desktop-title { display: block; }
.mobile-header { display: none; }

.icon-btn {
    background: transparent; border: none; cursor: pointer; width: 34px; height: 34px;
    border-radius: var(--radius-md); display: flex; align-items: center; justify-content: center;
    transition: var(--transition-interactive);
    color: var(--text-secondary);
}
.icon-btn:hover { background-color: var(--surface-hover); transform: rotate(8deg); color: var(--text-primary); }
.icon-btn:active { transform: scale(0.92); transition-duration: var(--duration-press); }
.icon-btn svg { width: 19px; height: 19px; fill: currentColor; transition: fill var(--duration-micro) var(--ease-standard); }

.new-chat-btn {
    background-color: var(--accent-color);
    color: var(--accent-text);
    border: 1px solid var(--accent-color);
    padding: 12px 14px;
    border-radius: var(--radius-md);
    font-family: var(--font-display);
    font-size: 15px; font-weight: 600; letter-spacing: 0.2px;
    cursor: pointer;
    transition: var(--transition-interactive);
    margin-bottom: 18px;
    flex-shrink: 0;
    box-shadow: var(--shadow-soft);
    display: flex; align-items: center; justify-content: center; gap: 8px;
    position: relative;
    overflow: hidden;
}
.new-chat-btn::after {
    content: '';
    position: absolute; inset: 0;
    background: linear-gradient(120deg, transparent 30%, rgba(255,255,255,0.10) 50%, transparent 70%);
    transform: translateX(-100%);
    transition: transform var(--duration-enter) var(--ease-out-expo);
}
.new-chat-btn:hover { background-color: var(--accent-hover); transform: translateY(-2px); box-shadow: var(--shadow-soft-accent); border-color: var(--accent-hover); }
.new-chat-btn:hover::after { transform: translateX(100%); }
.new-chat-btn:active { transform: translateY(0) scale(0.97); transition-duration: var(--duration-press); }

.chat-list {
    flex: 1; overflow-y: auto; display: flex; flex-direction: column; gap: 3px;
    margin-bottom: 10px; padding-right: 2px;
    mask-image: linear-gradient(to bottom, transparent 0, #000 6px, #000 calc(100% - 6px), transparent 100%);
    -webkit-mask-image: linear-gradient(to bottom, transparent 0, #000 6px, #000 calc(100% - 6px), transparent 100%);
}
/* Empty state when no chats exist — CSS-only since list is JS-rendered */
.chat-list:empty::before {
    content: '还没有对话';
    color: var(--text-muted);
    font-size: 13px;
    text-align: center;
    padding: 28px 16px;
    display: block;
    user-select: none;
    opacity: 0.7;
}

.chat-item {
    padding: 10px 30px 10px 12px; border-radius: var(--radius-md); cursor: pointer;
    transition: var(--transition-interactive);
    font-size: 14px; line-height: 1.4;
    white-space: nowrap; overflow: hidden; text-overflow: ellipsis;
    color: var(--text-secondary); border: 1px solid transparent; position: relative;
}
.chat-item::before {
    content: '';
    position: absolute; left: 4px; top: 50%;
    transform: translateY(-50%) scaleY(0);
    width: 3px; height: 56%;
    background: var(--accent-color); border-radius: 0 4px 4px 0;
    transition: transform var(--duration-micro) var(--ease-standard);
}
.chat-item:hover { background-color: var(--surface-hover); color: var(--text-primary); }
.chat-item:active { transform: scale(0.985); transition-duration: var(--duration-press); }
.chat-item.active {
    background-color: var(--accent-soft);
    color: var(--text-primary);
    font-weight: 600;
    border-color: transparent;
}
.chat-item.active::before { transform: translateY(-50%) scaleY(1); left: 0; }

.delete-chat-btn {
    position: absolute; right: 6px; top: 50%; transform: translateY(-50%);
    display: flex; opacity: 0;
    background: transparent; border: none; cursor: pointer;
    color: var(--text-muted); padding: 5px;
    border-radius: 5px;
    transition: opacity var(--duration-micro) var(--ease-standard), color var(--duration-micro) var(--ease-standard), background-color var(--duration-micro) var(--ease-standard);
}
.chat-item:hover .delete-chat-btn { opacity: 1; }
.delete-chat-btn:hover { color: var(--danger); background: color-mix(in srgb, var(--danger) 12%, transparent); }
.delete-chat-btn:active { transform: translateY(-50%) scale(0.88); transition-duration: var(--duration-press); }
.delete-chat-btn svg { width: 14px; height: 14px; fill: currentColor; }

.sidebar-backdrop {
    position: fixed;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    background: var(--backdrop-overlay);
    backdrop-filter: blur(0px);
    -webkit-backdrop-filter: blur(0px);
    z-index: 9;
    opacity: 0;
    visibility: hidden;
    pointer-events: none;
    transition: opacity var(--duration-enter) var(--ease-out-expo),
                backdrop-filter var(--duration-enter) var(--ease-out-expo),
                -webkit-backdrop-filter var(--duration-enter) var(--ease-out-expo),
                visibility var(--duration-enter);
}
.sidebar-backdrop.show {
    opacity: 1;
    visibility: visible;
    pointer-events: auto;
    backdrop-filter: blur(8px);
    -webkit-backdrop-filter: blur(8px);
}
.sidebar-backdrop.exiting {
    transition-duration: var(--duration-exit);
    transition-timing-function: var(--ease-in-expo);
}