:root {
    --primary-gradient: linear-gradient(135deg, #667eea 0%, #764ba2 100%);
    --glass-bg: rgba(255, 255, 255, 0.1);
    --glass-border: rgba(255, 255, 255, 0.2);
    --text-color: #ffffff;
    --text-secondary: rgba(255, 255, 255, 0.7);
    --btn-bg: rgba(255, 255, 255, 0.05);
    --btn-hover: rgba(255, 255, 255, 0.2);
    --btn-active: rgba(255, 255, 255, 0.3);
    --operator-color: #ff9f43;
    --equals-bg: #e17055;
}

* {
    box-sizing: border-box;
    font-family: 'Outfit', sans-serif;
    margin: 0;
    padding: 0;
}

body {
    background: var(--primary-gradient);
    min-height: 100vh;
    display: flex;
    justify-content: center;
    align-items: center;
    overflow: hidden;
}

.calculator-container {
    background: var(--glass-bg);
    backdrop-filter: blur(16px);
    -webkit-backdrop-filter: blur(16px);
    border: 1px solid var(--glass-border);
    border-radius: 24px;
    padding: 20px;
    box-shadow: 0 8px 32px 0 rgba(31, 38, 135, 0.37);
    width: 350px;
    transform: perspective(1000px) rotateX(2deg) rotateY(-2deg);
    transition: transform 0.3s ease;
}

.calculator-container:hover {
    transform: perspective(1000px) rotateX(0deg) rotateY(0deg);
}

.display {
    background: rgba(0, 0, 0, 0.2);
    border-radius: 12px;
    padding: 20px;
    margin-bottom: 20px;
    text-align: right;
    display: flex;
    flex-direction: column;
    justify-content: space-around;
    height: 100px;
}

.previous-operand {
    color: var(--text-secondary);
    font-size: 1rem;
    height: 20px;
}

.current-operand {
    color: var(--text-color);
    font-size: 2.5rem;
    font-weight: 600;
    word-wrap: break-word;
    word-break: break-all;
}

.buttons {
    display: grid;
    grid-template-columns: repeat(4, 1fr);
    gap: 12px;
}

.btn {
    background: var(--btn-bg);
    border: 1px solid var(--glass-border);
    border-radius: 12px;
    height: 60px;
    font-size: 1.25rem;
    color: var(--text-color);
    cursor: pointer;
    transition:  all 0.2s ease;
}

.btn:hover {
    background: var(--btn-hover);
    transform: translateY(-2px);
    box-shadow: 0 4px 12px rgba(0, 0, 0, 0.1);
}

.btn:active {
    background: var(--btn-active);
    transform: translateY(0px);
}

.span-two {
    grid-column: span 2;
}

.operator {
    color: var(--operator-color);
    font-weight: 600;
}

.equals {
    background: var(--equals-bg);
    border: none;
    font-weight: 600;
}

.equals:hover {
    background: #fab1a0;
}

/* Modal Styles */
.modal {
    position: fixed;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    background: rgba(0, 0, 0, 0.6);
    backdrop-filter: blur(5px);
    display: flex;
    justify-content: center;
    align-items: center;
    opacity: 1;
    visibility: visible;
    transition: opacity 0.3s ease, visibility 0.3s ease;
    z-index: 100;
}

.modal.hidden {
    opacity: 0;
    visibility: hidden;
    pointer-events: none;
}

.modal-content {
    background: #1e272e;
    padding: 30px;
    border-radius: 16px;
    width: 90%;
    max-width: 400px;
    text-align: center;
    color: white;
    box-shadow: 0 10px 40px rgba(0, 0, 0, 0.5);
    position: relative;
    border: 1px solid var(--glass-border);
}

.close-btn {
    position: absolute;
    top: 15px;
    right: 20px;
    font-size: 24px;
    cursor: pointer;
    color: var(--text-secondary);
}

.close-btn:hover {
    color: var(--text-color);
}

.modal-content h2 {
    margin-bottom: 10px;
    font-weight: 600;
}

.modal-content p {
    color: var(--text-secondary);
    margin-bottom: 20px;
}

.modal-content input {
    width: 100%;
    padding: 12px;
    border-radius: 8px;
    border: 1px solid #333;
    background: #2d3436;
    color: white;
    margin-bottom: 15px;
    font-size: 1rem;
    outline: none;
}

.modal-content input:focus {
    border-color: #764ba2;
}

.modal-content button#auth-btn {
    width: 100%;
    padding: 12px;
    border-radius: 8px;
    border: none;
    background: linear-gradient(135deg, #667eea 0%, #764ba2 100%);
    color: white;
    font-size: 1rem;
    cursor: pointer;
    font-weight: 600;
    transition: opacity 0.2s;
}

.modal-content button#auth-btn:hover {
    opacity: 0.9;
}

.token-box {
    background: #2d3436;
    padding: 10px;
    border-radius: 8px;
    display: flex;
    align-items: center;
    justify-content: space-between;
    margin-top: 10px;
    border: 1px solid #444;
}

.token-box code {
    font-family: monospace;
    color: #00cec9;
    overflow: hidden;
    text-overflow: ellipsis;
    white-space: nowrap;
    max-width: 250px;
}

.copy-btn {
    background: none;
    border: 1px solid #764ba2;
    color: #764ba2;
    padding: 5px 10px;
    border-radius: 4px;
    cursor: pointer;
    font-size: 0.8rem;
}

.copy-btn:hover {
    background: #764ba2;
    color: white;
}

.hidden {
    display: none !important;
}

.error {
    color: #ff7675;
    margin-top: 10px;
    font-size: 0.9rem;
}

.success {
    color: #00b894;
    font-weight: 600;
}

.small {
    font-size: 0.8rem;
    margin-top: 5px;
}