header {
    position: fixed;
    top: 0;
    left: 0;
    width: 100%;
    background-color: rgba(13, 27, 42, 0.95);
    backdrop-filter: blur(5px);
    z-index: 100;
    height: var(--header-height);
    display: flex;
    align-items: center;
    box-shadow: 0 4px 20px rgba(0, 0, 0, 0.3);
}

nav {
    max-width: 1200px;
    width: 100%;
    margin: 0 auto;
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding: 0 2rem;
}

.logo {
    font-size: 1.5rem;
    font-weight: 700;
    color: var(--accent-color);
    text-decoration: none;
    transition: color 0.3s;
}
.logo:hover {
    color: var(--secondary-accent);
}

.nav-links {
    display: flex;
    list-style: none;
}

.nav-links li {
    margin-left: 2rem;
}

.nav-links a {
    color: var(--text-white);
    text-decoration: none;
    font-weight: 500;
    position: relative;
    transition: color 0.3s;
}

.nav-links a:hover {
    color: var(--accent-color);
}

.nav-links a::after {
    content: '';
    position: absolute;
    width: 0;
    height: 2px;
    bottom: -5px;
    left: 0;
    background-color: var(--accent-color);
    transition: width 0.3s;
}

.nav-links a:hover::after {
    width: 100%;
}

section {
    max-width: 1200px;
    margin: 0 auto;
    padding: 6rem 2rem;
}

.section-title {
    font-size: 2rem;
    margin-bottom: 3rem;
    position: relative;
    display: inline-block;
    color: var(--accent-color);
}

.section-title::after {
    content: '';
    position: absolute;
    height: 2px;
    width: 70%;
    bottom: -10px;
    left: 0;
    background: linear-gradient(90deg, var(--accent-color), transparent);
}

footer {
    text-align: center;
    padding: 2rem;
    background-color: var(--medium-blue);
    margin-top: 4rem;
    position: relative;
}

.social-links {
    display: flex;
    justify-content: center;
    margin-bottom: 1rem;
}

.social-icon {
    display: flex;
    align-items: center;
    justify-content: center;
    height: 40px;
    width: 40px;
    border-radius: 50%;
    background-color: var(--dark-blue);
    color: var(--accent-color);
    margin: 0 0.5rem;
    font-size: 1.1rem;
    transition: transform 0.3s, background-color 0.3s, color 0.3s;
}

.social-icon:hover {
    transform: translateY(-3px);
    background-color: var(--accent-color);
    color: var(--dark-blue);
}

.copyright {
    color: var(--text-light);
    font-size: 0.9rem;
}

.back-to-top-button {
    position: fixed;
    bottom: 25px;
    right: 25px;
    z-index: 999;

    display: inline-flex;
    align-items: center;
    overflow: hidden;
    white-space: nowrap;
    text-decoration: none;
    cursor: pointer;

    background-color: var(--medium-blue);
    color: var(--accent-color);
    border: 2px solid var(--accent-color);
    border-radius: 50px;
    padding: 0.7rem 1rem;
    font-weight: 500;
    font-size: 0.9rem;
    box-shadow: 0 4px 12px rgba(0, 0, 0, 0.3);

    opacity: 0;
    visibility: hidden;
    transform: translateY(20px);
    transition: opacity 0.4s ease, visibility 0.4s ease, transform 0.4s ease,
                width 0.4s ease-in-out, padding 0.4s ease-in-out,
                background-color 0.3s ease, color 0.3s ease, box-shadow 0.3s ease;
}

.back-to-top-button:not(.hidden) {
    opacity: 1;
    visibility: visible;
    transform: translateY(0);
}

.back-to-top-button i {
    font-size: 1.1rem;
    line-height: 1;
    transition: margin 0.4s ease-in-out;
}

.back-to-top-button .button-text {
    display: inline-block;
    vertical-align: middle;
    max-width: 0;
    opacity: 0;
    margin-left: 0;
    transition: max-width 0.4s ease-in-out, opacity 0.3s ease-in 0.1s, margin-left 0.4s ease-in-out;
}

.back-to-top-button:hover,
.back-to-top-button:focus {
    background-color: var(--accent-color);
    color: var(--dark-blue);
    box-shadow: 0 6px 16px rgba(0, 0, 0, 0.4);
    outline: none;
}

.back-to-top-button:hover .button-text,
.back-to-top-button:focus .button-text {
    max-width: 150px;
    opacity: 1;
    margin-left: 0.6rem;
}

@media screen and (max-width: 600px) {
    .back-to-top-button {
        bottom: 15px;
        right: 15px;
        padding: 0.6rem 0.8rem;
    }

}