* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
}

body {
    background: #000000;
    color: #ffffff;
    font-family: 'Courier New', monospace;
    min-height: 100vh;
    display: flex;
    flex-direction: column;
    align-items: center;
    justify-content: flex-start;
    padding: 20px 20px 80px 20px;
}

/* TOP HEADER */
.top-header {
    position: sticky;
    top: 0;
    left: 0;
    right: 0;
    background: #000000;
    border-bottom: 1px solid #333333;
    display: flex;
    flex-direction: column;
    justify-content: center;
    align-items: center;
    padding: 15px 25px;
    z-index: 1000;
    width: 100%;
    box-shadow: 0 2px 10px rgba(0, 0, 0, 0.5);
}

.header-title {
    font-size: 20px;
    font-weight: bold;
    color: #ffffff;
    text-shadow: 0 0 10px rgba(255, 255, 255, 0.1);
    margin-bottom: 2px;
}

.header-subtitle {
    font-size: 12px;
    color: #666666;
    font-weight: normal;
}

/* CALCULATOR */
.calculator {
    background: #000000;
    border: 2px solid #ffffff;
    border-radius: 25px;
    padding: 25px;
    box-shadow:
        0 0 20px rgba(255, 255, 255, 0.1),
        inset 0 0 10px rgba(255, 255, 255, 0.05);
    max-width: 320px;
    width: 100%;
    margin-top: 20px;
}

.display {
    background: #000000;
    border: 2px solid #ffffff;
    border-radius: 15px;
    padding: 15px 12px;
    margin-bottom: 15px;
    min-height: 60px;
    display: flex;
    flex-direction: column;
    justify-content: center;
    text-align: right;
    box-shadow: inset 0 0 10px rgba(255, 255, 255, 0.1);
}

.expression {
    color: #666666;
    font-size: 12px;
    min-height: 14px;
    margin-bottom: 4px;
    white-space: nowrap;
    overflow: hidden;
    text-overflow: ellipsis;
}

.result {
    color: #ffffff;
    font-size: 24px;
    font-weight: bold;
    min-height: 30px;
    display: flex;
    align-items: center;
    justify-content: flex-end;
    text-shadow: 0 0 5px rgba(255, 255, 255, 0.1);
    white-space: nowrap;
    overflow: hidden;
    text-overflow: clip;
}

.buttons {
    display: flex;
    flex-direction: column;
    gap: 6px;
}

.button-row {
    display: grid;
    grid-template-columns: repeat(4, 1fr);
    gap: 6px;
}

/* BASE BUTTONS */
.btn {
    background: #000000;
    color: #ffffff;
    border: 1px solid #ffffff;
    border-radius: 12px;
    padding: 14px 8px;
    font-size: 16px;
    font-family: 'Courier New', monospace;
    cursor: pointer;
    box-shadow: 0 0 5px rgba(255, 255, 255, 0.1);
    min-height: 48px;
    display: flex;
    align-items: center;
    justify-content: center;
}

.btn.zero {
    grid-column: span 2;
}

/* COLORED BUTTON VARIANTS */
.btn.clear {
    color: #ff6666;
    border-color: #ff6666;
}

.btn.operator {
    color: #66aaff;
    border-color: #66aaff;
}

.btn.function {
    color: #66ff66;
    border-color: #66ff66;
}

.btn.equals {
    color: #ffff66;
    border-color: #ffff66;
}

/* HOVER EFFECTS FOR DEVICES WITH MOUSE */
.btn:hover {
    background: #ffffff;
    color: #000000;
    border-color: #ffffff;
    transform: translateY(-1px);
    box-shadow: 0 0 20px rgba(255, 255, 255, 0.6);
}

.btn.clear:hover {
    background: #ff6666;
    color: #000000;
    border-color: #ff6666;
    box-shadow: 0 0 20px rgba(255, 102, 102, 0.6);
}

.btn.operator:hover {
    background: #66aaff;
    color: #000000;
    border-color: #66aaff;
    box-shadow: 0 0 20px rgba(102, 170, 255, 0.6);
}

.btn.function:hover {
    background: #66ff66;
    color: #000000;
    border-color: #66ff66;
    box-shadow: 0 0 20px rgba(102, 255, 102, 0.6);
}

.btn.equals:hover {
    background: #ffff66;
    color: #000000;
    border-color: #ffff66;
    box-shadow: 0 0 20px rgba(255, 255, 102, 0.6);
}


@media (hover: none) and (pointer: coarse) {

    /* ACTIVE EFFECTS FOR DEVICES WITH TOUCH */
    .btn:active {
        background: #ffffff;
        color: #000000;
        border-color: #ffffff;
        transform: translateY(-1px);
        box-shadow: 0 0 20px rgba(255, 255, 255, 0.6);
    }

    .btn.clear:active {
        background: #ff6666;
        color: #000000;
        border-color: #ff6666;
        box-shadow: 0 0 20px rgba(255, 102, 102, 0.6);
    }

    .btn.operator:active {
        background: #66aaff;
        color: #000000;
        border-color: #66aaff;
        box-shadow: 0 0 20px rgba(102, 170, 255, 0.6);
    }

    .btn.function:active {
        background: #66ff66;
        color: #000000;
        border-color: #66ff66;
        box-shadow: 0 0 20px rgba(102, 255, 102, 0.6);
    }

    .btn.equals:active {
        background: #ffff66;
        color: #000000;
        border-color: #ffff66;
        box-shadow: 0 0 20px rgba(255, 255, 102, 0.6);
    }
}


.btn {
    position: relative;
    overflow: visible;
}

@keyframes buttonPulse {
    0% {
        box-shadow: 0 0 5px rgba(255, 255, 255, 0.1);
    }

    50% {
        box-shadow: 0 0 30px rgba(255, 255, 255, 0.8);
    }

    100% {
        box-shadow: 0 0 5px rgba(255, 255, 255, 0.1);
    }
}

/* EXPLANATION SECTION */
.explanation-section {
    margin-top: 50px;
    margin-bottom: 50px;
    max-width: 800px;
    width: 100%;
}

.explanation-container {
    background: #000000;
    border: 1px solid #333333;
    border-radius: 20px;
    padding: 30px;
    box-shadow: 0 0 8px rgba(255, 255, 255, 0.1);
}

.explanation-container:hover {
    border-color: #ffffff;
    box-shadow: 0 0 40px rgba(255, 255, 255, 0.6);
    transform: scale(1.02);
}

.explanation-header {
    text-align: center;
    margin-bottom: 30px;
}

.explanation-title {
    color: #ffffff;
    font-size: 20px;
    margin-bottom: 10px;
}

.explanation-subtitle {
    color: #666666;
    font-size: 14px;
    font-weight: normal;
}

.explanation-content {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(300px, 1fr));
    gap: 20px;
}

.explanation-card {
    background: #000000;
    border: 1px solid #333333;
    border-radius: 15px;
    padding: 20px;
    cursor: pointer;
}

.explanation-card:hover {
    background: #ffffff;
    color: #000000;
    border-color: #ffffff;
    transform: translateY(-5px) scale(1.05);
    box-shadow: 0 8px 20px rgba(255, 255, 255, 0.6);
}

.explanation-card h3 {
    color: #ffffff;
    font-size: 16px;
    margin-bottom: 10px;
}

.explanation-card:hover h3 {
    color: #000000;
}

.explanation-card p {
    color: #cccccc;
    font-size: 14px;
    line-height: 1.5;
    transition: color 0.05s ease;
}

.explanation-card:hover p {
    color: #333333;
}

/* BOTTOM DONATION BAR */
.donation-header {
    position: fixed;
    bottom: 0;
    left: 0;
    right: 0;
    background: #000000;
    border-top: 1px solid #333333;
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding: 10px 20px;
    z-index: 1000;
    width: 100%;
    box-shadow: 0 -2px 10px rgba(0, 0, 0, 0.5);
}

.donation-text {
    color: #666666;
    font-size: 14px;
    font-style: italic;
    flex-grow: 1;
}

.donation-btn {
    background: #000000;
    color: #ffffff;
    border: 1px solid #ffffff;
    border-radius: 15px;
    padding: 8px 14px;
    font-size: 11px;
    font-family: 'Courier New', monospace;
    cursor: pointer;
    white-space: nowrap;
}

.donation-btn:hover {
    background: #ffffff;
    color: #000000;
    border-color: #ffffff;
    transform: translateY(-1px);
    box-shadow: 0 0 15px rgba(255, 255, 255, 0.4);
}

.donation-btn:active {
    transform: translateY(0);
}

/* HIDE TOP-BAR (NOW INTEGRATED INTO HEADER) */
.top-bar {
    display: none;
}

/* MOBILE RESPONSIVE */
@media (max-width: 480px) {
    body {
        padding: 15px 15px 60px 15px;
    }

    .top-header {
        padding: 12px 15px;
    }

    .header-title {
        font-size: 18px;
    }

    .header-subtitle {
        font-size: 11px;
    }

    .calculator {
        padding: 20px;
        border-radius: 20px;
    }

    .btn {
        padding: 12px 8px;
        font-size: 14px;
        min-height: 44px;
    }

    .result {
        font-size: 22px;
    }

    .explanation-content {
        grid-template-columns: 1fr;
    }

    .donation-header {
        padding: 8px 15px;
    }

    .donation-text {
        font-size: 12px;
    }

    .donation-btn {
        font-size: 10px;
        padding: 6px 10px;
    }
}

/* DISABLE HOVER ON TOUCH DEVICES */
@media (hover: none) {
    .btn:hover {
        background: #000000;
        color: inherit;
        border-color: inherit;
        transform: none;
        box-shadow: 0 0 5px rgba(255, 255, 255, 0.1);
    }

    .explanation-card:hover {
        background: #000000;
        color: inherit;
        border-color: #333333;
        transform: none;
        box-shadow: none;
    }

    .explanation-card:hover h3 {
        color: #ffffff;
    }

    .explanation-card:hover p {
        color: #cccccc;
    }

    .explanation-container:hover {
        border-color: #333333;
        box-shadow: 0 0 10px rgba(255, 255, 255, 0.1);
        transform: none;
    }

    .donation-btn:hover {
        background: #000000;
        color: #ffffff;
        border-color: #ffffff;
        transform: none;
        box-shadow: none;
    }
}

@keyframes glitch {
    0% {
        transform: rotate(0deg);
    }

    20% {
        transform: rotate(3deg);
    }

    40% {
        transform: rotate(-2deg);
    }

    60% {
        transform: rotate(4deg);
    }

    80% {
        transform: rotate(-3deg);
    }

    100% {
        transform: rotate(0deg);
    }
}