:root {
    --background: #0A0C0F;
    --primary-color: #1E1F24;
    --secondary-color: #6B7280;
    --accent-color: #10B981;
    --accent-hover: #059669;
    --danger-color: #EF4444;
    --danger-hover: #DC2626;
    --text-color: #F3F4F6;
    --text-muted: #9CA3AF;
    --border-radius-sm: 8px;
    --border-radius-md: 12px;
    --border-radius-lg: 1000px;
    --transition: all 0.2s cubic-bezier(0.4, 0, 0.2, 1);
    --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);
}

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

html {
    font-family: 'Inter', -apple-system, BlinkMacSystemFont, 'Segoe UI', sans-serif;
    font-size: 16px;
    color: var(--text-color);
}

body {
    min-height: 100vh;
    padding: 20px;
    background: linear-gradient(135deg, var(--background) 0%, #15171C 100%);
    display: flex;
    flex-direction: column;
    align-items: center;
}

h1 {
    margin-top: 60px;
    margin-bottom: 40px;
    font-size: 3.5rem;
    font-weight: 700;
    letter-spacing: -0.02em;
    text-align: center;
    background: linear-gradient(135deg, var(--accent-color) 0%, #34D399 100%);
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    background-clip: text;
    animation: fadeIn 0.5s ease-out;
}

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

.wrapper {
    width: 700px;
    max-width: 100%;
    display: flex;
    flex-direction: column;
    gap: 16px;
}

form {
    position: relative;
    width: 100%;
    animation: slideUp 0.4s ease-out;
}

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

#todo-input {
    box-sizing: border-box;
    padding: 16px 24px;
    width: 100%;
    background: var(--primary-color);
    border: 2px solid transparent;
    border-radius: var(--border-radius-lg);
    color: var(--text-color);
    font-size: 1rem;
    transition: var(--transition);
    box-shadow: var(--shadow-md);
}

#todo-input:hover {
    background: #25262C;
}

#todo-input:focus {
    outline: none;
    border-color: var(--accent-color);
    box-shadow: 0 0 0 3px rgba(16, 185, 129, 0.2);
}

#todo-input::placeholder {
    color: var(--text-muted);
    font-weight: 400;
}

#add-button {
    position: absolute;
    top: 6px;
    right: 6px;
    background: var(--accent-color);
    height: calc(100% - 12px);
    padding: 0 32px;
    border: none;
    border-radius: 1000px;
    font-weight: 600;
    font-size: 0.95rem;
    color: white;
    cursor: pointer;
    transition: var(--transition);
    letter-spacing: 0.025em;
    text-transform: uppercase;
    box-shadow: var(--shadow-sm);
}

#add-button:hover {
    background: var(--accent-hover);
    transform: scale(1.02);
}

#add-button:active {
    transform: scale(0.98);
}

.todo {
    margin-bottom: 12px;
    padding: 8px 16px 8px 20px;
    background: var(--primary-color);
    border-radius: var(--border-radius-md);
    display: flex;
    align-items: center;
    gap: 12px;
    transition: var(--transition);
    box-shadow: var(--shadow-md);
    border: 1px solid transparent;
    animation: fadeIn 0.3s ease-out;
}

.todo:hover {
    transform: translateX(4px);
    border-color: var(--accent-color);
    box-shadow: var(--shadow-lg);
    background: #25262C;
}

.todo .todo-text {
    padding: 14px 8px 14px 0;
    flex-grow: 1;
    font-size: 1rem;
    line-height: 1.5;
    transition: var(--transition);
}

.delete-button {
    padding: 8px;
    background: none;
    border: none;
    border-radius: var(--border-radius-sm);
    display: flex;
    justify-content: center;
    align-items: center;
    cursor: pointer;
    transition: var(--transition);
}

.delete-button:hover {
    background: rgba(239, 68, 68, 0.1);
}

.delete-button svg {
    width: 20px;
    height: 20px;
    fill: var(--text-muted);
    transition: var(--transition);
}

.delete-button:hover svg {
    fill: var(--danger-color);
    transform: scale(1.1);
}

.custom-checkbox {
    border: 2px solid var(--accent-color);
    border-radius: 50%;
    min-height: 24px;
    min-width: 24px;
    display: flex;
    justify-content: center;
    align-items: center;
    flex-shrink: 0;
    transition: var(--transition);
    cursor: pointer;
    background: transparent;
}

.custom-checkbox:hover {
    background: rgba(16, 185, 129, 0.1);
    transform: scale(1.05);
}

.custom-checkbox svg {
    width: 14px;
    height: 14px;
    fill: transparent;
    transition: var(--transition);
}

input[type="checkbox"]:checked ~ .custom-checkbox {
    background: var(--accent-color);
    border-color: var(--accent-color);
    transform: scale(1.05);
}

input[type="checkbox"]:checked ~ .custom-checkbox svg {
    fill: white;
}

input[type="checkbox"]:checked ~ .todo-text {
    text-decoration: line-through;
    color: var(--text-muted);
    opacity: 0.8;
}

input[type="checkbox"] {
    display: none;
}

.wrapper:empty::after {
    content: 'No tasks yet. Add one above!';
    display: block;
    text-align: center;
    color: var(--text-muted);
    padding: 40px 20px;
    font-size: 1.1rem;
    background: var(--primary-color);
    border-radius: var(--border-radius-md);
    border: 2px dashed var(--secondary-color);
    margin-top: 20px;
}

@media (max-width: 500px) {
    html {
        font-size: 14px;
    }
    
    body {
        padding: 16px;
    }
    
    h1 {
        margin-top: 40px;
        margin-bottom: 30px;
        font-size: 2.5rem;
    }
    
    #add-button {
        position: static;
        width: 100%;
        margin-top: 12px;
        padding: 14px;
        height: auto;
        top: auto;
        right: auto;
    }
    
    .todo {
        padding: 8px 12px 8px 16px;
    }
    
    .todo:hover {
        transform: none;
    }
    
    .custom-checkbox {
        min-height: 28px;
        min-width: 28px;
    }
    
    .delete-button svg {
        width: 24px;
        height: 24px;
    }
}

::-webkit-scrollbar {
    width: 10px;
}

::-webkit-scrollbar-track {
    background: var(--primary-color);
}

::-webkit-scrollbar-thumb {
    background: var(--secondary-color);
    border-radius: var(--border-radius-lg);
}

::-webkit-scrollbar-thumb:hover {
    background: var(--accent-color);
}

:focus-visible {
    outline: 3px solid var(--accent-color);
    outline-offset: 2px;
}