/* =========================
   App Header
   ========================= */

.app-header {
    position: sticky;
    top: 0;
    z-index: 1000;
    height: 90px;
    padding: 0 32px;
    display: flex;
    align-items: center;
    justify-content: left;
    background: var(--header-bg);
    backdrop-filter: blur(20px);
    -webkit-backdrop-filter: blur(20px);
    border-bottom: 1px solid rgba(42, 145, 204, 0.322);
    box-shadow: 0 4px 25px rgba(0, 0, 0, 0.3);
}

/* Title */

.app-header h1 {
    margin: 0;
    font-size: 20px;
    font-weight: 600;
    color: var(--header-text);
    letter-spacing: -0.02em;
}

/* Buttons */

.app-header button {
    position: relative;
    overflow: hidden;

    margin-left: 15px;
    padding: 10px 22px;
    border-radius: 8px;
    border: none;
    cursor: pointer;

    font-size: 15px;
    font-weight: 600;
    color: var(--header-text);

    outline: none;
    z-index: 0;
}

.app-header .start-btn {
    background: var(--header-start-btn-bg);
}

.app-header .stop-btn {
    background: var(--header-stop-btn-bg);
}

.app-header .back-btn {
    background: var(--header-back-btn-bg);
}

.app-header .theme-btn {
    background: var(--header-theme-btn-bg);
    color: var(--header-theme-btn);
    display: inline-flex;
    align-items: center;
    gap: 6px;
}

/* Buttons animations */

.app-header button:not(:disabled)::before {
    content: "";
    position: absolute;
    inset: 0;

    background-size: 200% 200%;
    background-position: 0% 50%;

    animation: gradientMove 1s ease infinite;

    opacity: 0;
    transition: opacity 0.5s ease;

    z-index: -1;
}

.app-header .start-btn:not(:disabled)::before {
    background: var(--header-start-btn-bg-before);
}

.app-header .stop-btn:not(:disabled)::before {
    background: var(--header-stop-btn-bg-before);
}

.app-header .back-btn:not(:disabled)::before {
    background: var(--header-back-btn-bg-before);
}

.app-header .theme-btn:not(:disabled)::before {
    background: var(--header-theme-btn-bg-before);
}

.app-header button:not(:disabled):hover::before,
.app-header button:not(:disabled):focus-visible::before {
    opacity: 1;
}

@keyframes gradientMove {
    0%   { background-position:   0% 50%; }
    50%  { background-position: 100% 50%; }
    100% { background-position:   0% 50%; }
}

/* Buttons disabled */

.app-header button:disabled {
    background: var(--header-btn-disabled-bg);
    color: var(--header-btn-disabled);;
    cursor: not-allowed;
    box-shadow: none;
}

/* Responsive */

@media (max-width: 768px) {

    .app-header {
        flex-wrap: wrap;
        height: auto;
        padding: 12px 16px;
        gap: 10px;
    }

    .app-header img {
        width: 60px;
    }

    .app-header .start-btn,
    .app-header .stop-btn {
        flex: 1;
        margin-left: 0;
    }

    .app-header .start-btn,
    .app-header .stop-btn {
        margin-top: 8px;
    }

    .app-header .back-btn,
    .app-header h1 {
        display: none;
    }

    .app-header .theme-btn {
        width: 36px;
        height: 36px;
        padding: 0;
        margin-left: auto;

        border-radius: 50%;

        display: flex;
        align-items: center;
        justify-content: center;
    }

    .app-header .theme-btn .theme-text {
        display: none;
    }

    .app-header .theme-btn .theme-icon {
        font-size: 18px;
        line-height: 1;
    }
}