:root {
    --bg-gradient-start: #f8f9fa;
    --bg-gradient-end: #e9ecef;
    --text-color: #212529;
    --box-bg: rgba(255, 255, 255, 0.9);
    --box-shadow: rgba(0, 0, 0, 0.1);
    --input-border-color: #ced4da;
    --input-focus-label-color: #007bff;
    --button-bg: #007bff;
    --button-hover-bg: #0056b3;
    --link-color: #007bff;
    --error-bg: rgba(220, 53, 69, 0.2);
    --error-text-color: #dc3545;
    --info-bg: rgba(25, 135, 84, 0.2);
    --theme-switcher-bg: rgba(0, 0, 0, 0.1);
}

html[data-theme='dark'] {
    --bg-gradient-start: #2c3e50;
    --bg-gradient-end: #4ca1af;
    --text-color: #ecf0f1;
    --box-bg: rgba(0, 0, 0, 0.7);
    --box-shadow: rgba(0, 0, 0, 0.8);
    --input-border-color: #bdc3c7;
    --input-focus-label-color: #1abc9c;
    --button-bg: #16a085;
    --button-hover-bg: #1abc9c;
    --link-color: #1abc9c;
    --error-bg: rgba(231, 76, 60, 0.3);
    --info-bg: rgba(26, 188, 156, 0.3);
    --theme-switcher-bg: rgba(255, 255, 255, 0.1);
}

body {
    margin: 0;
    padding: 20px;
    font-family: sans-serif;
    background: linear-gradient(to right, var(--bg-gradient-start), var(--bg-gradient-end));
    display: flex;
    justify-content: center;
    align-items: center;
    min-height: 100vh;
    color: var(--text-color);
    transition: background 0.5s, color 0.5s;
    box-sizing: border-box;
}

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

.login-box {
    animation: fadeInDown 0.5s ease-out;
    background: var(--box-bg);
    padding: 40px;
    border-radius: 10px;
    box-shadow: 0 15px 25px var(--box-shadow);
    width: 100%;
    max-width: 400px;
    text-align: center;
    transition: background 0.5s, box-shadow 0.5s;
}

.login-box h2 {
    margin: 0 0 30px;
    padding: 0;
    color: var(--text-color);
    text-align: center;
}

.login-illustration {
    display: block;
    margin: 0 auto 20px;
    max-width: 120px;
    height: auto;
    filter: drop-shadow(0 0 5px rgba(0, 123, 255, 0.5));
    transition: transform 0.3s ease;
}

.login-illustration:hover {
    transform: scale(1.05) rotate(5deg);
}

.login-box .user-box {
    position: relative;
    margin-bottom: 30px;
}

.login-box .user-box input {
    width: 100%;
    padding: 10px 0;
    font-size: 16px;
    color: var(--text-color);
    border: none;
    border-bottom: 1px solid var(--input-border-color);
    outline: none;
    background: transparent;
}

.login-box .user-box label {
    position: absolute;
    top: 0;
    right: 0;
    padding: 10px 0;
    font-size: 16px;
    color: var(--text-color);
    pointer-events: none;
    transition: .5s;
}

.login-box .user-box input:focus ~ label,
.back-to-home {
    display: block;
    text-align: center;
    margin-top: 20px;
    color: var(--text-color);
    font-size: 0.9em;
    opacity: 0.8;
    transition: all 0.3s ease;
}

.back-to-home:hover {
    opacity: 1;
    color: var(--link-color);
    transform: translateX(-5px);
}

.back-to-home svg {
    vertical-align: middle;
    margin-left: 5px;
    width: 16px;
    height: 16px;
    fill: currentColor;
}

.login-box button[type="submit"] {
    position: relative;
    overflow: hidden;
    background: var(--button-bg);
    border: none;
    outline: none;
    color: #fff;
    padding: 10px 20px;
    cursor: pointer;
    border-radius: 5px;
    font-size: 16px;
    text-transform: uppercase;
    letter-spacing: 2px;
    margin-top: 20px;
    transition: .5s;
}

.login-box button[type="submit"]:hover {
    background: var(--button-hover-bg);
    color: #fff;
    box-shadow: 0 0 5px var(--button-hover-bg),
                0 0 25px var(--button-hover-bg);
}

.ripple {
    position: absolute;
    border-radius: 50%;
    background: rgba(255, 255, 255, 0.6);
    transform: scale(0);
    animation: ripple 0.6s linear;
}

@keyframes ripple {
    to {
        transform: scale(4);
        opacity: 0;
    }
}

.error, .info {
    color: var(--text-color);
    padding: 10px;
    border-radius: 5px;
    margin-bottom: 20px;
    text-align: center;
}

.error {
    background: var(--error-bg);
}

.info {
    background: var(--info-bg);
}

.remember-me {
    display: flex;
    align-items: center;
    margin-top: 15px;
    font-size: 0.9em;
    justify-content: center;
}

.remember-me label {
    margin-right: 5px;
    color: var(--text-color);
}

a {
    color: var(--link-color);
    text-decoration: none;
}

.theme-switcher {
    position: absolute;
    top: 20px;
    left: 20px;
    cursor: pointer;
    font-size: 24px;
    background: var(--theme-switcher-bg);
    padding: 5px 10px;
    border-radius: 50%;
    z-index: 1000;
}

.user-box .error-message {
    color: var(--error-text-color);
    font-size: 0.8em;
    position: absolute;
    bottom: -20px;
    right: 0;
    display: none;
}

@keyframes fadeIn {
    from { opacity: 0; }
    to { opacity: 1; }
}

.user-box.error .error-message {
    display: block;
    animation: fadeIn 0.3s ease-out;
}

.user-box.error input {
    border-bottom-color: var(--error-text-color);
}

@media (max-width: 480px) {
    .login-box {
        padding: 20px;
    }
    .login-box h2 {
        font-size: 1.8em;
    }
}