body {
  margin: 0;
  font-family: Arial, sans-serif;
  background: #f4f7fa;
  color: #1f2937;
}
.site-header {
  background: #ffffff;
  border-bottom: 1px solid #e5e7eb;
}
.container {
  max-width: 1024px;
  margin: 0 auto;
  padding: 0 20px;
}
.brand-bar {
  display: flex;
  align-items: center;
  justify-content: space-between;
  min-height: 110px;
}
.logo-image {
  width: 300px;
  height: 90px;
  object-fit: contain;
}
nav {
  display: flex;
  gap: 16px;
  flex-wrap: wrap;
}
nav a {
  display: inline-block;
  padding: 12px 18px;
  color: #1d4ed8;
  text-decoration: none;
  font-weight: 600;
  border-radius: 10px;
  transition: background 0.2s ease, color 0.2s ease;
}
nav a:hover {
  background: #1d4ed8;
  color: #ffffff;
}
main {
  padding: 30px 0 50px;
}
.hero,
.content {
  background: #ffffff;
  border-radius: 18px;
  padding: 40px;
  box-shadow: 0 12px 30px rgba(15, 23, 42, 0.08);
}
.content {
  padding: 32px;
}
.hero h1 {
  margin-top: 0;
  font-size: 2.5rem;
  line-height: 1.1;
}
.hero p {
  max-width: 680px;
  font-size: 1rem;
  line-height: 1.7;
  color: #4b5563;
}
.section-card {
  margin-top: 24px;
  display: grid;
  gap: 18px;
}
.section-card a {
  display: block;
  padding: 22px;
  background: #ffffff;
  border-radius: 16px;
  text-decoration: none;
  color: #111827;
  box-shadow: 0 8px 22px rgba(15, 23, 42, 0.05);
  transition: transform 0.2s ease, box-shadow 0.2s ease;
}
.section-card a:hover {
  transform: translateY(-2px);
  box-shadow: 0 12px 28px rgba(15, 23, 42, 0.1);
}

/* Homepage card hover: very light gray background and subtle outer shadow */
.hero .card,
.hero a.card,
.hero .card .card-body,
.hero a.card .card-body {
    transition: background-color 0.18s ease, box-shadow 0.18s ease, transform 0.18s ease;
    background-clip: padding-box;
}
.hero a.card:hover,
.hero .card:hover,
.hero a.card:focus,
.hero .card:focus,
.hero a.card:active,
.hero .card:active {
    background-color: #f5f6f7;
    box-shadow: 0 10px 30px rgba(15, 23, 42, 0.12);
    transform: translateY(-3px);
}
.hero .card .card-body,
.hero a.card .card-body {
    background: transparent;
}
.section-card h2 {
  margin: 0 0 10px;
}
h1 {
  margin-top: 0;
}
.topic-list {
  margin: 24px 0 0;
  padding-left: 20px;
}
footer {
  text-align: center;
  padding: 24px 0 40px;
  color: #6b7280;
}

.video-table a {
  color: #1d4ed8;
  text-decoration: none;
}
.video-table a:hover {
  text-decoration: underline;
}

.video-thumb {
  width: 60px;
  max-width: 100%;
  height: auto;
  border-radius: 8px;
  display: block;
}
.video-table td {
  vertical-align: middle;
}


.nav {
    --bs-nav-link-padding-x: 1rem;
    --bs-nav-link-padding-y: 0.5rem;
    --bs-nav-link-color: var(--bs-link-color);
    --bs-nav-link-hover-color: var(--bs-link-hover-color);
    --bs-nav-link-disabled-color: var(--bs-secondary-color);
    display: flex;
    flex-wrap: wrap;
    padding-left: 0;
    margin-bottom: 0;
    list-style:none
}

.nav-link {
    display: block;
    padding: var(--bs-nav-link-padding-y) var(--bs-nav-link-padding-x);
    font-size: var(--bs-nav-link-font-size);
    font-weight: var(--bs-nav-link-font-weight);
    color: var(--bs-nav-link-color);
    text-decoration: none;
    background: 0 0;
    border: 0;
    transition:color .15s ease-in-out, background-color .15s ease-in-out, border-color .15s ease-in-out
}

@media (prefers-reduced-motion: reduce) {
    .nav-link {
        transition:none
    }
}

.nav-link:focus, .nav-link:hover {
    color:var(--bs-nav-link-hover-color)
}

.nav-link:focus-visible {
    outline: 0;
    box-shadow:0 0 0 .25rem rgba(13, 110, 253, .25)
}

.nav-link.disabled, .nav-link:disabled {
    color: var(--bs-nav-link-disabled-color);
    pointer-events: none;
    cursor:default
}

.nav-tabs {
    --bs-nav-tabs-border-width: var(--bs-border-width);
    --bs-nav-tabs-border-color: var(--bs-border-color);
    --bs-nav-tabs-border-radius: var(--bs-border-radius);
    --bs-nav-tabs-link-hover-border-color: var(--bs-secondary-bg) var(--bs-secondary-bg) var(--bs-border-color);
    --bs-nav-tabs-link-active-color: var(--bs-emphasis-color);
    --bs-nav-tabs-link-active-bg: var(--bs-body-bg);
    --bs-nav-tabs-link-active-border-color: var(--bs-border-color) var(--bs-border-color) var(--bs-body-bg);
    border-bottom:var(--bs-nav-tabs-border-width) solid var(--bs-nav-tabs-border-color)
}

.nav-tabs .nav-link {
    margin-bottom: calc(-1 * var(--bs-nav-tabs-border-width));
    border: var(--bs-nav-tabs-border-width) solid transparent;
    border-top-left-radius: var(--bs-nav-tabs-border-radius);
    border-top-right-radius:var(--bs-nav-tabs-border-radius)
}

.nav-tabs .nav-link:focus, .nav-tabs .nav-link:hover {
    isolation: isolate;
    border-color:var(--bs-nav-tabs-link-hover-border-color)
}

.nav-tabs .nav-item.show .nav-link, .nav-tabs .nav-link.active {
    color: var(--bs-nav-tabs-link-active-color);
    background-color: var(--bs-nav-tabs-link-active-bg);
    border-color:var(--bs-nav-tabs-link-active-border-color)
}

.nav-tabs .dropdown-menu {
    margin-top: calc(-1 * var(--bs-nav-tabs-border-width));
    border-top-left-radius: 0;
    border-top-right-radius:0
}

.nav-pills {
    --bs-nav-pills-border-radius: var(--bs-border-radius);
    --bs-nav-pills-link-active-color: #fff;
    --bs-nav-pills-link-active-bg:#0d6efd
}

.nav-pills .nav-link {
    border-radius:var(--bs-nav-pills-border-radius)
}

.nav-pills .nav-link.active, .nav-pills .show > .nav-link {
    color: var(--bs-nav-pills-link-active-color);
    background-color:var(--bs-nav-pills-link-active-bg)
}

.nav-underline {
    --bs-nav-underline-gap: 1rem;
    --bs-nav-underline-border-width: 0.125rem;
    --bs-nav-underline-link-active-color: var(--bs-emphasis-color);
    gap:var(--bs-nav-underline-gap)
}

.nav-underline .nav-link {
    padding-right: 0;
    padding-left: 0;
    border-bottom:var(--bs-nav-underline-border-width) solid transparent
}

.nav-underline .nav-link:focus, .nav-underline .nav-link:hover {
    border-bottom-color:currentcolor
}

.nav-underline .nav-link.active, .nav-underline .show > .nav-link {
    font-weight: 700;
    color: var(--bs-nav-underline-link-active-color);
    border-bottom-color:currentcolor
}

.nav-fill .nav-item, .nav-fill > .nav-link {
    flex: 1 1 auto;
    text-align:center
}

.nav-justified .nav-item, .nav-justified > .nav-link {
    flex-grow: 1;
    flex-basis: 0;
    text-align:center
}

.nav-fill .nav-item .nav-link, .nav-justified .nav-item .nav-link {
    width:100%
}

.tab-content > .tab-pane {
    display:none
}

.tab-content > .active {
    display:block
}

.navbar {
    --bs-navbar-padding-x: 0;
    --bs-navbar-padding-y: 0.5rem;
    --bs-navbar-color: rgba(var(--bs-emphasis-color-rgb), 0.65);
    --bs-navbar-hover-color: rgba(var(--bs-emphasis-color-rgb), 0.8);
    --bs-navbar-disabled-color: rgba(var(--bs-emphasis-color-rgb), 0.3);
    --bs-navbar-active-color: rgba(var(--bs-emphasis-color-rgb), 1);
    --bs-navbar-brand-padding-y: 0.3125rem;
    --bs-navbar-brand-margin-end: 1rem;
    --bs-navbar-brand-font-size: 1.25rem;
    --bs-navbar-brand-color: rgba(var(--bs-emphasis-color-rgb), 1);
    --bs-navbar-brand-hover-color: rgba(var(--bs-emphasis-color-rgb), 1);
    --bs-navbar-nav-link-padding-x: 0.5rem;
    --bs-navbar-toggler-padding-y: 0.25rem;
    --bs-navbar-toggler-padding-x: 0.75rem;
    --bs-navbar-toggler-font-size: 1.25rem;
    --bs-navbar-toggler-icon-bg: url("data:image/svg+xml,%3csvg xmlns='http://www.w3.org/2000/svg' viewBox='0 0 30 30'%3e%3cpath stroke='rgba%2833, 37, 41, 0.75%29' stroke-linecap='round' stroke-miterlimit='10' stroke-width='2' d='M4 7h22M4 15h22M4 23h22'/%3e%3c/svg%3e");
    --bs-navbar-toggler-border-color: rgba(var(--bs-emphasis-color-rgb), 0.15);
    --bs-navbar-toggler-border-radius: var(--bs-border-radius);
    --bs-navbar-toggler-focus-width: 0.25rem;
    --bs-navbar-toggler-transition: box-shadow 0.15s ease-in-out;
    position: relative;
    display: flex;
    flex-wrap: wrap;
    align-items: center;
    justify-content: space-between;
    padding:var(--bs-navbar-padding-y) var(--bs-navbar-padding-x)
}

.navbar > .container, .navbar > .container-fluid, .navbar > .container-lg, .navbar > .container-md, .navbar > .container-sm, .navbar > .container-xl, .navbar > .container-xxl {
    display: flex;
    flex-wrap: inherit;
    align-items: center;
    justify-content:space-between
}

.navbar-brand {
    padding-top: var(--bs-navbar-brand-padding-y);
    padding-bottom: var(--bs-navbar-brand-padding-y);
    margin-right: var(--bs-navbar-brand-margin-end);
    font-size: var(--bs-navbar-brand-font-size);
    color: var(--bs-navbar-brand-color);
    text-decoration: none;
    white-space:nowrap
}

.navbar-brand:focus, .navbar-brand:hover {
    color:var(--bs-navbar-brand-hover-color)
}

.navbar-nav {
    --bs-nav-link-padding-x: 0;
    --bs-nav-link-padding-y: 0.5rem;
    --bs-nav-link-color: var(--bs-navbar-color);
    --bs-nav-link-hover-color: var(--bs-navbar-hover-color);
    --bs-nav-link-disabled-color: var(--bs-navbar-disabled-color);
    display: flex;
    flex-direction: column;
    padding-left: 0;
    margin-bottom: 0;
    list-style:none
}

.navbar-nav .nav-link.active, .navbar-nav .nav-link.show {
    color:var(--bs-navbar-active-color)
}

.navbar-nav .dropdown-menu {
    position:static
}

.navbar-text {
    padding-top: .5rem;
    padding-bottom: .5rem;
    color:var(--bs-navbar-color)
}

.navbar-text a, .navbar-text a:focus, .navbar-text a:hover {
    color:var(--bs-navbar-active-color)
}

.navbar-collapse {
    flex-grow: 1;
    flex-basis: 100%;
    align-items:center
}

.navbar-toggler {
    padding: var(--bs-navbar-toggler-padding-y) var(--bs-navbar-toggler-padding-x);
    font-size: var(--bs-navbar-toggler-font-size);
    line-height: 1;
    color: var(--bs-navbar-color);
    background-color: transparent;
    border: var(--bs-border-width) solid var(--bs-navbar-toggler-border-color);
    border-radius: var(--bs-navbar-toggler-border-radius);
    transition:var(--bs-navbar-toggler-transition)
}

@media (prefers-reduced-motion: reduce) {
    .navbar-toggler {
        transition:none
    }
}

.navbar-toggler:hover {
    text-decoration:none
}

.navbar-toggler:focus {
    text-decoration: none;
    outline: 0;
    box-shadow:0 0 0 var(--bs-navbar-toggler-focus-width)
}

.navbar-toggler-icon {
    display: inline-block;
    width: 1.5em;
    height: 1.5em;
    vertical-align: middle;
    background-image: var(--bs-navbar-toggler-icon-bg);
    background-repeat: no-repeat;
    background-position: center;
    background-size:100%
}

.navbar-nav-scroll {
    max-height: var(--bs-scroll-height, 75vh);
    overflow-y:auto
}

@media (min-width: 576px) {
    .navbar-expand-sm {
        flex-wrap: nowrap;
        justify-content:flex-start
    }

    .navbar-expand-sm .navbar-nav {
        flex-direction:row
    }

    .navbar-expand-sm .navbar-nav .dropdown-menu {
        position:absolute
    }

    .navbar-expand-sm .navbar-nav .nav-link {
        padding-right: var(--bs-navbar-nav-link-padding-x);
        padding-left:var(--bs-navbar-nav-link-padding-x)
    }

    .navbar-expand-sm .navbar-nav-scroll {
        overflow:visible
    }

    .navbar-expand-sm .navbar-collapse {
        display: flex !important;
        flex-basis:auto
    }

    .navbar-expand-sm .navbar-toggler {
        display:none
    }

    .navbar-expand-sm .offcanvas {
        position: static;
        z-index: auto;
        flex-grow: 1;
        width: auto !important;
        height: auto !important;
        visibility: visible !important;
        background-color: transparent !important;
        border: 0 !important;
        transform: none !important;
        transition:none
    }

    .navbar-expand-sm .offcanvas .offcanvas-header {
        display:none
    }

    .navbar-expand-sm .offcanvas .offcanvas-body {
        display: flex;
        flex-grow: 0;
        padding: 0;
        overflow-y:visible
    }
}

@media (min-width: 768px) {
    .navbar-expand-md {
        flex-wrap: nowrap;
        justify-content:flex-start
    }

    .navbar-expand-md .navbar-nav {
        flex-direction:row
    }

    .navbar-expand-md .navbar-nav .dropdown-menu {
        position:absolute
    }

    .navbar-expand-md .navbar-nav .nav-link {
        padding-right: var(--bs-navbar-nav-link-padding-x);
        padding-left:var(--bs-navbar-nav-link-padding-x)
    }

    .navbar-expand-md .navbar-nav-scroll {
        overflow:visible
    }

    .navbar-expand-md .navbar-collapse {
        display: flex !important;
        flex-basis:auto
    }

    .navbar-expand-md .navbar-toggler {
        display:none
    }

    .navbar-expand-md .offcanvas {
        position: static;
        z-index: auto;
        flex-grow: 1;
        width: auto !important;
        height: auto !important;
        visibility: visible !important;
        background-color: transparent !important;
        border: 0 !important;
        transform: none !important;
        transition:none
    }

    .navbar-expand-md .offcanvas .offcanvas-header {
        display:none
    }

    .navbar-expand-md .offcanvas .offcanvas-body {
        display: flex;
        flex-grow: 0;
        padding: 0;
        overflow-y:visible
    }
}

@media (min-width: 992px) {
    .navbar-expand-lg {
        flex-wrap: nowrap;
        justify-content:flex-start
    }

    .navbar-expand-lg .navbar-nav {
        flex-direction:row
    }

    .navbar-expand-lg .navbar-nav .dropdown-menu {
        position:absolute
    }

    .navbar-expand-lg .navbar-nav .nav-link {
        padding-right: var(--bs-navbar-nav-link-padding-x);
        padding-left:var(--bs-navbar-nav-link-padding-x)
    }

    .navbar-expand-lg .navbar-nav-scroll {
        overflow:visible
    }

    .navbar-expand-lg .navbar-collapse {
        display: flex !important;
        flex-basis:auto
    }

    .navbar-expand-lg .navbar-toggler {
        display:none
    }

    .navbar-expand-lg .offcanvas {
        position: static;
        z-index: auto;
        flex-grow: 1;
        width: auto !important;
        height: auto !important;
        visibility: visible !important;
        background-color: transparent !important;
        border: 0 !important;
        transform: none !important;
        transition:none
    }

    .navbar-expand-lg .offcanvas .offcanvas-header {
        display:none
    }

    .navbar-expand-lg .offcanvas .offcanvas-body {
        display: flex;
        flex-grow: 0;
        padding: 0;
        overflow-y:visible
    }
}

@media (min-width: 1200px) {
    .navbar-expand-xl {
        flex-wrap: nowrap;
        justify-content:flex-start
    }

    .navbar-expand-xl .navbar-nav {
        flex-direction:row
    }

    .navbar-expand-xl .navbar-nav .dropdown-menu {
        position:absolute
    }

    .navbar-expand-xl .navbar-nav .nav-link {
        padding-right: var(--bs-navbar-nav-link-padding-x);
        padding-left:var(--bs-navbar-nav-link-padding-x)
    }

    .navbar-expand-xl .navbar-nav-scroll {
        overflow:visible
    }

    .navbar-expand-xl .navbar-collapse {
        display: flex !important;
        flex-basis:auto
    }

    .navbar-expand-xl .navbar-toggler {
        display:none
    }

    .navbar-expand-xl .offcanvas {
        position: static;
        z-index: auto;
        flex-grow: 1;
        width: auto !important;
        height: auto !important;
        visibility: visible !important;
        background-color: transparent !important;
        border: 0 !important;
        transform: none !important;
        transition:none
    }

    .navbar-expand-xl .offcanvas .offcanvas-header {
        display:none
    }

    .navbar-expand-xl .offcanvas .offcanvas-body {
        display: flex;
        flex-grow: 0;
        padding: 0;
        overflow-y:visible
    }
}

@media (min-width: 1400px) {
    .navbar-expand-xxl {
        flex-wrap: nowrap;
        justify-content:flex-start
    }

    .navbar-expand-xxl .navbar-nav {
        flex-direction:row
    }

    .navbar-expand-xxl .navbar-nav .dropdown-menu {
        position:absolute
    }

    .navbar-expand-xxl .navbar-nav .nav-link {
        padding-right: var(--bs-navbar-nav-link-padding-x);
        padding-left:var(--bs-navbar-nav-link-padding-x)
    }

    .navbar-expand-xxl .navbar-nav-scroll {
        overflow:visible
    }

    .navbar-expand-xxl .navbar-collapse {
        display: flex !important;
        flex-basis:auto
    }

    .navbar-expand-xxl .navbar-toggler {
        display:none
    }

    .navbar-expand-xxl .offcanvas {
        position: static;
        z-index: auto;
        flex-grow: 1;
        width: auto !important;
        height: auto !important;
        visibility: visible !important;
        background-color: transparent !important;
        border: 0 !important;
        transform: none !important;
        transition:none
    }

    .navbar-expand-xxl .offcanvas .offcanvas-header {
        display:none
    }

    .navbar-expand-xxl .offcanvas .offcanvas-body {
        display: flex;
        flex-grow: 0;
        padding: 0;
        overflow-y:visible
    }
}

.navbar-expand {
    flex-wrap: nowrap;
    justify-content:flex-start
}

.navbar-expand .navbar-nav {
    flex-direction:row
}

.navbar-expand .navbar-nav .dropdown-menu {
    position:absolute
}

.navbar-expand .navbar-nav .nav-link {
    padding-right: var(--bs-navbar-nav-link-padding-x);
    padding-left:var(--bs-navbar-nav-link-padding-x)
}

.navbar-expand .navbar-nav-scroll {
    overflow:visible
}

.navbar-expand .navbar-collapse {
    display: flex !important;
    flex-basis:auto
}

.navbar-expand .navbar-toggler {
    display:none
}

.navbar-expand .offcanvas {
    position: static;
    z-index: auto;
    flex-grow: 1;
    width: auto !important;
    height: auto !important;
    visibility: visible !important;
    background-color: transparent !important;
    border: 0 !important;
    transform: none !important;
    transition:none
}

.navbar-expand .offcanvas .offcanvas-header {
    display:none
}

.navbar-expand .offcanvas .offcanvas-body {
    display: flex;
    flex-grow: 0;
    padding: 0;
    overflow-y:visible
}

.navbar-dark, .navbar[data-bs-theme=dark] {
    --bs-navbar-color: rgba(255, 255, 255, 0.55);
    --bs-navbar-hover-color: rgba(255, 255, 255, 0.75);
    --bs-navbar-disabled-color: rgba(255, 255, 255, 0.25);
    --bs-navbar-active-color: #fff;
    --bs-navbar-brand-color: #fff;
    --bs-navbar-brand-hover-color: #fff;
    --bs-navbar-toggler-border-color: rgba(255, 255, 255, 0.1);
    --bs-navbar-toggler-icon-bg: url("data:image/svg+xml,%3csvg xmlns='http://www.w3.org/2000/svg' viewBox='0 0 30 30'%3e%3cpath stroke='rgba%28255, 255, 255, 0.55%29' stroke-linecap='round' stroke-miterlimit='10' stroke-width='2' d='M4 7h22M4 15h22M4 23h22'/%3e%3c/svg%3e")
}

[data-bs-theme=dark] .navbar-toggler-icon {
    --bs-navbar-toggler-icon-bg: url("data:image/svg+xml,%3csvg xmlns='http://www.w3.org/2000/svg' viewBox='0 0 30 30'%3e%3cpath stroke='rgba%28255, 255, 255, 0.55%29' stroke-linecap='round' stroke-miterlimit='10' stroke-width='2' d='M4 7h22M4 15h22M4 23h22'/%3e%3c/svg%3e")
}