body {
    background-color: #f8f9fa;
    font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, "Helvetica Neue", Arial, sans-serif;
}

.sidebar {
    background-color: #fff;
    box-shadow: 2px 0 5px rgba(0,0,0,0.1);
    height: 100vh;
    overflow-y: auto;
    position: fixed;
    width: 25%;
    z-index: 1000;
}

.main-content {
    margin-left: 25%;
    padding: 2rem;
}

.player-container {
    background-color: #fff;
    border-radius: 10px;
    box-shadow: 0 0 15px rgba(0,0,0,0.1);
    padding: 2rem;
    margin-top: 2rem;
}

.current-playing {
    text-align: center;
}

.audio-player {
    margin-top: 2rem;
}

audio {
    width: 100%;
    max-width: 600px;
}

.list-group-item {
    border: none;
    padding: 0.75rem 1.25rem;
    transition: all 0.2s;
    position: relative;
    font-size: 0.9rem;
    line-height: 1.2;
}

.list-group-item:hover {
    background-color: #f8f9fa;
    transform: translateX(5px);
}

.list-group-item.active {
    background-color: #007bff;
    border-color: #007bff;
}

.unit-title {
    color: #007bff;
    margin: 1rem 0;
    padding-left: 1rem;
    font-size: 1rem;
}

.unit-content {
    padding-left: 1rem;
}

.accordion-button:not(.collapsed) {
    background-color: #e7f1ff;
    color: #007bff;
}

.accordion-button:focus {
    box-shadow: none;
    border-color: rgba(0,0,0,.125);
}

/* 添加工具提示样式 */
.list-group-item[data-tooltip] {
    position: relative;
}

.list-group-item[data-tooltip]::after {
    content: attr(data-tooltip);
    position: fixed;
    left: 25%;
    top: 50%;
    transform: translate(20px, -50%);
    background-color: rgba(0, 0, 0, 0.8);
    color: white;
    padding: 4px 8px;
    border-radius: 4px;
    font-size: 12px;
    white-space: nowrap;
    visibility: hidden;
    opacity: 0;
    transition: opacity 0.2s, visibility 0.2s;
    z-index: 1050;
    pointer-events: none;
}

.list-group-item[data-tooltip]:hover::after {
    visibility: visible;
    opacity: 1;
}

/* Mobile Optimization */
@media (max-width: 768px) {
    .sidebar {
        position: relative;
        width: 100%;
        height: auto;
        max-height: 50vh;
    }
    
    .main-content {
        margin-left: 0;
        padding: 1rem;
    }

    .player-container {
        position: fixed;
        bottom: 0;
        left: 0;
        right: 0;
        margin: 0;
        padding: 1rem;
        border-radius: 10px 10px 0 0;
        background-color: rgba(255, 255, 255, 0.95);
        backdrop-filter: blur(10px);
        z-index: 1001;
    }

    .list-group-item {
        padding: 0.5rem 1rem;
        font-size: 0.95rem;
    }

    .unit-title {
        font-size: 0.95rem;
        margin: 0.5rem 0;
    }

    audio {
        width: 100%;
        margin: 0 auto;
    }

    .current-playing {
        margin-bottom: 0.5rem;
    }

    #nowPlaying {
        font-size: 1rem;
        margin: 0;
        white-space: nowrap;
        overflow: hidden;
        text-overflow: ellipsis;
    }

    .list-group-item[data-tooltip]::after {
        position: absolute;
        left: auto;
        right: 0;
        top: 100%;
        transform: none;
        margin-top: 5px;
        font-size: 10px;
        background-color: rgba(0, 0, 0, 0.9);
        white-space: normal;
        max-width: 200px;
        word-break: break-all;
    }

    body {
        padding-bottom: 160px;
    }

    .accordion-button {
        padding: 0.75rem 1rem;
    }

    .accordion-body {
        padding: 0.5rem;
    }
}

.unit-group .accordion {
    margin: 0.5rem 0;
}

.unit-group .accordion-item {
    border: none;
    background: transparent;
}

.unit-group .accordion-button {
    background: transparent;
    padding: 0.5rem 1rem;
    font-size: 0.95rem;
    color: #007bff;
}

.unit-group .accordion-button:not(.collapsed) {
    background-color: transparent;
    color: #0056b3;
}

.unit-group .accordion-button::after {
    width: 0.8rem;
    height: 0.8rem;
    background-size: 0.8rem;
}

.unit-group .accordion-body {
    padding: 0.5rem;
}

/* Mobile Optimization */
@media (max-width: 768px) {
    .unit-group .accordion-button {
        padding: 0.4rem 0.8rem;
        font-size: 0.9rem;
    }

    .unit-group .accordion-body {
        padding: 0.3rem;
    }
}