@import url('https://fonts.googleapis.com/css2?family=Inter:wght@300;400;500;600;700&display=swap');

body {
    font-family: 'Inter', -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif, "Apple Color Emoji", "Segoe UI Emoji", "Segoe UI Symbol";
    scroll-behavior: smooth;
}

.symbol {
    color: #38bdf8; /* sky-400 */
    font-weight: 500; /* medium */
}

#main-header {
    /* Background handled by Tailwind bg-black/70 backdrop-blur-md */
}

#main-header.scrolled {
    box-shadow: 0 4px 20px rgba(0,0,0,0.5); /* Darker, larger shadow for depth */
}

.nav-link.active {
    color: #FFFFFF; 
    font-weight: 600;
}

.section-title {
    font-size: 2.25rem; /* text-4xl approx */
    line-height: 2.75rem;
    font-weight: 700; /* bold */
    color: #F3F4F6; /* gray-100 */
    margin-bottom: 3.5rem; 
    padding-bottom: 1rem;
    border-bottom: 1px solid #374151; /* gray-700 */
    display: inline-block;
}
@media (min-width: 768px) { /* md breakpoint */
    .section-title {
        font-size: 3rem; /* text-5xl approx */
        line-height: 1.1;
    }
}

.subsection-title {
    font-size: 1.5rem; /* text-2xl approx */
    line-height: 2rem;
    font-weight: 600; /* semibold */
    color: #E5E7EB; /* gray-200 */
    margin-bottom: 1.5rem; 
    margin-top: 2.5rem; 
}
.subsection-title:first-of-type { 
    margin-top: 0;
}
@media (min-width: 768px) { /* md breakpoint */
    .subsection-title {
        font-size: 1.875rem; /* text-3xl approx */
        line-height: 2.25rem;
    }
}

.equation-block {
    background-color: rgba(31, 41, 55, 0.7); /* gray-800 with opacity */
    border: 1px solid #4B5563; /* gray-600 */
    padding: 1.25rem 1.75rem;
    border-radius: 0.75rem; /* rounded-xl */
    font-family: 'SFMono-Regular', Consolas, 'Liberation Mono', Menlo, Courier, monospace;
    font-size: 1rem; /* text-base */
    color: #D1D5DB; /* gray-300 */
    overflow-x: auto;
    margin-bottom: 0.75rem;
    box-shadow: 0 4px 10px rgba(0,0,0,0.2);
    transition: all 0.3s ease-in-out;
}

.equation-block:hover {
    border-color: #38bdf8; /* sky-400 */
    box-shadow: 0 0 20px rgba(56, 189, 248, 0.15);
}

.equation-desc {
    font-size: 0.875rem; /* 14px */
    color: #9CA3AF; /* gray-400 */
    margin-left: 1.75rem;
    font-style: italic;
}

.equation-inline {
    font-family: 'SFMono-Regular', Consolas, 'Liberation Mono', Menlo, Courier, monospace;
    color: #93c5fd; /* blue-300 */
    background-color: rgba(55, 65, 81, 0.8); /* gray-700 with opacity */
    padding: 0.2em 0.45em;
    border-radius: 0.3rem;
    font-size: 0.9em; 
    display: inline-block;
    vertical-align: baseline;
}

.animate-on-scroll {
    opacity: 0;
    transform: translateY(25px) scale(0.97);
    transition: opacity 0.7s cubic-bezier(0.645, 0.045, 0.355, 1), transform 0.7s cubic-bezier(0.645, 0.045, 0.355, 1);
}

.animate-on-scroll.is-visible {
    opacity: 1;
    transform: translateY(0) scale(1);
}

::-webkit-scrollbar {
    width: 8px;
    height: 8px;
}

::-webkit-scrollbar-track {
    background: transparent; 
}

::-webkit-scrollbar-thumb {
    background: #374151; /* gray-700 */
    border-radius: 4px;
    border: 2px solid transparent; /* For padding effect */
    background-clip: padding-box;
}

::-webkit-scrollbar-thumb:hover {
    background: #4B5563; /* gray-600 */
}