/* ===========================
   CSS Reset & Base Styles
   =========================== */

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

:root {
    --color-black: #000000;
    --color-white: #ffffff;
    --color-gray-100: #f5f5f5;
    --color-gray-200: #e5e5e5;
    --color-gray-300: #d4d4d4;
    --color-gray-400: #a3a3a3;
    --color-gray-500: #737373;
    --color-gray-600: #525252;
    --color-gray-700: #404040;
    --color-gray-800: #262626;
    --color-gray-900: #171717;

    --shadow-sm: 0 1px 2px 0 rgba(0, 0, 0, 0.05);
    --shadow-md: 0 4px 6px -1px rgba(0, 0, 0, 0.1);
    --shadow-lg: 0 10px 15px -3px rgba(0, 0, 0, 0.1);
    --shadow-xl: 0 20px 25px -5px rgba(0, 0, 0, 0.1);

    --transition-fast: 150ms ease;
    --transition-base: 300ms ease;
    --transition-slow: 500ms ease;
}

body {
    font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, 'Helvetica Neue', Arial, sans-serif;
    background-color: var(--color-white);
    color: var(--color-black);
    line-height: 1.6;
    min-height: 100vh;
    display: flex;
    flex-direction: column;
    -webkit-font-smoothing: antialiased;
    -moz-osx-font-smoothing: grayscale;
}

/* ===========================
   Container & Layout
   =========================== */

.container {
    flex: 1;
    display: flex;
    flex-direction: column;
    justify-content: center;
    align-items: center;
    padding: 2rem 1rem;
    min-height: 100vh;
}

.login-card {
    width: 100%;
    max-width: 420px;
    background: var(--color-white);
    border: 1px solid var(--color-gray-200);
    border-radius: 8px;
    padding: 3rem 2rem;
    box-shadow: var(--shadow-xl);
    animation: fadeIn 0.5s ease;
}

@keyframes fadeIn {
    from {
        opacity: 0;
        transform: translateY(20px);
    }
    to {
        opacity: 1;
        transform: translateY(0);
    }
}

/* ===========================
   Logo Section
   =========================== */

.logo-section {
    text-align: center;
    margin-bottom: 2.5rem;
}

.logo {
    font-size: 2rem;
    font-weight: 700;
    letter-spacing: -0.02em;
    margin-bottom: 0.5rem;
    color: var(--color-black);
}

.tagline {
    font-size: 0.95rem;
    color: var(--color-gray-500);
    font-weight: 400;
}

/* ===========================
   Form Styles
   =========================== */

.login-form,
.otp-form {
    display: flex;
    flex-direction: column;
    gap: 1.5rem;
}

.form-group {
    display: flex;
    flex-direction: column;
    gap: 0.5rem;
}

label {
    font-size: 0.875rem;
    font-weight: 500;
    color: var(--color-gray-700);
}

input[type="email"],
input[type="tel"] {
    width: 100%;
    padding: 0.75rem 1rem;
    font-size: 1rem;
    border: 1px solid var(--color-gray-300);
    border-radius: 6px;
    background: var(--color-white);
    color: var(--color-black);
    transition: all var(--transition-fast);
}

input[type="email"]:focus,
input[type="tel"]:focus {
    outline: none;
    border-color: var(--color-black);
    box-shadow: 0 0 0 3px rgba(0, 0, 0, 0.05);
}

input[type="email"]::placeholder,
input[type="tel"]::placeholder {
    color: var(--color-gray-400);
}

/* ===========================
   Tab Group
   =========================== */

.tab-group {
    display: flex;
    gap: 0.5rem;
    background: var(--color-gray-100);
    padding: 0.25rem;
    border-radius: 6px;
}

.tab {
    flex: 1;
    padding: 0.625rem 1rem;
    font-size: 0.875rem;
    font-weight: 500;
    border: none;
    border-radius: 4px;
    background: transparent;
    color: var(--color-gray-600);
    cursor: pointer;
    transition: all var(--transition-fast);
}

.tab:hover {
    color: var(--color-black);
}

.tab.active {
    background: var(--color-white);
    color: var(--color-black);
    box-shadow: var(--shadow-sm);
}

/* ===========================
   Buttons
   =========================== */

.submit-btn {
    width: 100%;
    padding: 0.875rem 1.5rem;
    font-size: 1rem;
    font-weight: 600;
    color: var(--color-white);
    background: var(--color-black);
    border: none;
    border-radius: 6px;
    cursor: pointer;
    transition: all var(--transition-fast);
    position: relative;
    display: flex;
    align-items: center;
    justify-content: center;
    gap: 0.5rem;
}

.submit-btn:hover {
    background: var(--color-gray-800);
    transform: translateY(-1px);
    box-shadow: var(--shadow-md);
}

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

.submit-btn:disabled {
    opacity: 0.6;
    cursor: not-allowed;
    transform: none;
}

.resend-btn {
    width: 100%;
    padding: 0.75rem 1.5rem;
    font-size: 0.875rem;
    font-weight: 500;
    color: var(--color-black);
    background: transparent;
    border: 1px solid var(--color-gray-300);
    border-radius: 6px;
    cursor: pointer;
    transition: all var(--transition-fast);
}

.resend-btn:hover {
    background: var(--color-gray-100);
    border-color: var(--color-black);
}

.back-btn {
    display: flex;
    align-items: center;
    gap: 0.5rem;
    font-size: 0.875rem;
    font-weight: 500;
    color: var(--color-gray-600);
    cursor: pointer;
    margin-bottom: 1.5rem;
    width: fit-content;
    transition: color var(--transition-fast);
}

.back-btn:hover {
    color: var(--color-black);
}

/* ===========================
   Button Loader
   =========================== */

.btn-loader {
    width: 16px;
    height: 16px;
    border: 2px solid var(--color-white);
    border-top-color: transparent;
    border-radius: 50%;
    animation: spin 0.6s linear infinite;
}

@keyframes spin {
    to { transform: rotate(360deg); }
}

/* ===========================
   OTP Section
   =========================== */

.otp-section {
    animation: fadeIn 0.5s ease;
}

.otp-title {
    font-size: 1.5rem;
    font-weight: 700;
    margin-bottom: 0.5rem;
    color: var(--color-black);
}

.otp-subtitle {
    font-size: 0.875rem;
    color: var(--color-gray-500);
    margin-bottom: 2rem;
}

.otp-subtitle span {
    color: var(--color-black);
    font-weight: 600;
}

.otp-inputs {
    display: flex;
    gap: 0.5rem;
    justify-content: center;
    margin-bottom: 1.5rem;
}

.otp-input {
    width: 3rem;
    height: 3.5rem;
    font-size: 1.5rem;
    font-weight: 600;
    text-align: center;
    border: 1px solid var(--color-gray-300);
    border-radius: 6px;
    background: var(--color-white);
    color: var(--color-black);
    transition: all var(--transition-fast);
}

.otp-input:focus {
    outline: none;
    border-color: var(--color-black);
    box-shadow: 0 0 0 3px rgba(0, 0, 0, 0.05);
}

/* ===========================
   Info & Footer
   =========================== */

.info-text {
    font-size: 0.8125rem;
    color: var(--color-gray-500);
    text-align: center;
    line-height: 1.5;
}

.footer {
    margin-top: 3rem;
    padding: 1rem;
    text-align: center;
}

.footer p {
    font-size: 0.75rem;
    color: var(--color-gray-400);
}

/* ===========================
   Utility Classes
   =========================== */

.hidden {
    display: none !important;
}

/* ===========================
   Responsive Design
   =========================== */

@media (max-width: 640px) {
    .login-card {
        padding: 2rem 1.5rem;
        border: none;
        box-shadow: none;
    }

    .logo {
        font-size: 1.75rem;
    }

    .otp-input {
        width: 2.5rem;
        height: 3rem;
        font-size: 1.25rem;
    }

    .otp-inputs {
        gap: 0.375rem;
    }
}

@media (max-width: 380px) {
    .otp-input {
        width: 2.25rem;
        height: 2.75rem;
        font-size: 1.125rem;
    }

    .container {
        padding: 1rem 0.75rem;
    }
}

/* ===========================
   Dark Mode Support (Optional)
   =========================== */

@media (prefers-color-scheme: dark) {
    /* Uncomment to enable dark mode
    :root {
        --color-black: #ffffff;
        --color-white: #000000;
    }

    body {
        background-color: #000000;
        color: #ffffff;
    }

    .login-card {
        background: #0a0a0a;
        border-color: #1a1a1a;
    }
    */
}