.music-theory-container{min-height:calc(100vh - var(--nav-height));margin-top:calc(-1*var(--space-xl));width:100%;display:flex;position:relative}.music-theory-container:before{content:"";top:0;bottom:calc(-1*var(--space-4xl));background-color:var(--card-bg,#1a1b26);border-right:1px solid var(--border-color,#2a2b36);z-index:0;width:224px;position:absolute;left:0}.music-theory-sidebar{background-color:var(--card-bg,#1a1b26);border-right:1px solid var(--border-color,#2a2b36);width:224px;top:var(--nav-height);height:calc(100vh - var(--nav-height));flex-direction:column;display:flex;position:sticky;overflow-y:auto}.sidebar-header{border-bottom:1px solid var(--border-color,#2a2b36);background-color:var(--card-bg,#1a1b26);z-index:10;padding:1.5rem;position:sticky;top:0}.sidebar-header h2{color:var(--text-base,#fff);margin:0;font-size:1.1rem}.sidebar-content{padding:1rem 0}.sidebar-chapter{margin-bottom:1.5rem}.chapter-title{text-transform:uppercase;letter-spacing:.05em;color:var(--text-muted,#888);margin-bottom:.5rem;padding:0 1.5rem;font-size:.75rem}.chapter-lessons{margin:0;padding:0;list-style:none}.lesson-link{color:var(--text-base,#e0e0e0);border-left:3px solid #0000;padding:.5rem 1.5rem;font-size:.85rem;text-decoration:none;transition:all .2s;display:block}.lesson-link:hover{background-color:var(--hover-bg,#ffffff0d);color:var(--accent-violet,#a855f7)}.lesson-link.active{background-color:var(--active-bg,#a855f71a);color:var(--accent-violet,#a855f7);border-left-color:var(--accent-violet,#a855f7);font-weight:500}.music-theory-main{z-index:1;flex:1;max-width:1200px;margin:0 auto;padding:2rem;position:relative}@media (max-width:768px){.music-theory-container{flex-direction:column}.music-theory-container:before{display:none}.music-theory-sidebar{border-right:none;border-bottom:1px solid var(--border-color,#2a2b36);width:100%;height:auto;position:relative;top:0}}