style.css

body {
    height: 100vh;
    display: flex;
    flex-direction: column;
    justify-content: center;
    align-items: center;
    background-color: whitesmoke;
}

p {
    text-align: center;
    font-size: 20px;
}

button {
    background-color: whitesmoke;
}

input {
    border: none;
    border-bottom: 1px solid gray;
    background-color: whitesmoke;
}

.dark-theme-body {
    background-color: #1E1E1E;
}

.dark-theme-username {
    color: white;
}

.counter-buttons {
    height: 55px;
    width: 55px;
    font-size: 35px;
    border-radius: 50%;
    border: none;
}

.dark-theme-input-container {
    color: white;
}

.dark-theme-input {
    background-color: #1E1E1E;
    color: white;
    border: none;
    border-bottom: 1px solid white;
}

#theme-button {
    position: fixed;
    top: 15px;
    right: 15px;
}

#counter-container {
    height: 275px;
    width: 300px;    
    border: 1px solid black;
    border-radius: 10px;
    box-sizing: border-box;
    padding-top: 15px;
    display: flex;
    flex-direction: column;
    align-items: center;
    background-color: #353535;
}

#counter {
    font-size: 40px;
    color: white;
}

#decrement {
    background-color: #FF3333;
    color: white;
}

#clear {
    background-color: #D3D3D3;
    color: white;
}

#increment {
    background-color: #46FF33;
    color: white;
}

#input-container {
    margin-top: 20px;
}